Ok, we talked about posting about the crazy, dangerous and stupid things we have seen done or done ourselves.  I have a few to post and will think back over what all I have seen or done too.
I mentioned the F96 slimline in HO fixture, which will get it started nicely!

I did electrical maintenance (as a side, weekend job) for a customer for years. His business grew and when he bought a vacant warehouse/office, I went through the whole place getting everything working.  The dock area, offices, warehouse/work area and storage warehouse were all 277v and the entire basement was 120v.  The storage warehouse was originally lit with 150w HPS fixtures, but only about 1/4 of them were working.  The warehouse work area was lit with F96HO fixtures.  This is where the main "interesting" things were found.  Several 277v ballasts had been replaced with 120v units.  I have no clue how they performed but they were dead, along with the lamps.  Several fixtures also had the F96 slimline lamps "installed" in them, with the single pin touching one contact inside the recessed double contact lampholders.  No clue how well they worked but the ends were badly burnt on the lamps.  The beauty was the ballast that was wired up with masking tape on the wires!  They had half ass twisted the wires together, then wrapped it with masking tape.  The 8 light circuit that this fixture was on would pop the breaker as soon as it was turned on.  After tracing it down, it was obvious as to why.  The tape had come off and the wires were all exposed and bare!  It had nearly started a fire before "welding" to the reflector!  Several other fixtures were later found with the same situation, except the power wires did not short out, just the output leads.
Other nice finds: Several F96 slimline ballasts wired in HO fixtures.  Blue leads all tied together with one wire nut, same for reds and yellows.  Needless to say: toasted ballast! In the office (suspended ceiling) fixtures, several had ballasts replaced and they had run the blue, red and yellow wires all to the same end of the fixture, from one ballast...ditto for the other end! The strange thing is it actually WORKED that way! There must have been 30 different brands, wattages and colors of lamps in those offices, all mixed up in random order.  Only about half the fixtures were working. 
I have encountered plenty more at other locations since.  Some favorites: F32T8 bulbs in F40T12 fixtures (short life and disgusting shimmer!), F96HO lamps in F96VHO fixtures (WAY overdriven (215 watts going to 110 watt lamp) and 34 watt lamps in preheat F40 fixtures.
Let's hear some other experiences yall have seen!

The only thing I am guilty of is mis-matching fluorescent colors. Usually I want to use up what lamps I have so I will install whatever I have on hand. Every few years I find a "new" favorite lamp and buy that lamp. When I have time, however, I will go back and do a better job of matching colors. I am even moving toward group replacement in some of the offices I maintain. Like you, I do some lighting maintenance on the side.

Usually I don't like seeing fluorescent colors mis-matched. Once in a while, however, there will be a legitimate reason to mix colors. I maintain the lights at a photography studio and they have some lights with different colored lamps. Some lights for general lighting have el-cheapo 34W lamps that look brown after a few years. Other lights have 40W Cool white plus that look very nice. Still others have cool white deluxe mixed with daylight for better CRI. The daylight are too blue by themselves but C50s would be too dim. Other lights do have C50 lamps where brightness is not critical. In this case, however, the light colors are intentionally mismatched and not just mismatched because I don't know any better!

-Nelson

At my high school, they are ruining vintage 24" T8 Duro-Test Vita-Lites with a cheapo Standard electronic ballast. In the 5 years I've been there, two have been run until vacuum loss, the two replacements are still in service, and they develop end blackening within 200 hrs. of use. 

I have a couple I came across:

1. A 175 watt MV lamp installed in a 250 watt MH pendant. Result... arc tube explosion.

2. 175 watt MH lamps installed in recessed lights ballasted for same wattage Mercury (H39). Result... arc tube explosions.

3. Several F96T12 fixtures with wire connections held together with electrical tape and pinched wires between housings and covers.

3. My favorite, unmounted F96 ballasts that fall when you take the cover off.

tmcdllr, I have seen that done with F96s also, or even worse, the ballast resting on the reflector as you say, but the reflector being held up by the lamps.  When you remove the lamps, the reflector and ballast both fall down!
Nogden, I mix colors in the same way you mention for a nice effect, but I just hate the random mixing of colors/wattages. It looks "half ass" to me.

Another thing I hate is when someone puts a bipin lamp in and does not get all four of the pins in the lampholders.  It lights up in a RS or IS circuit, but kills the lamp in a short time.

Here's some I came across:

Using HPS lamps in recessed 70W MH fixtures indoors, so when you walk in the lights go white-yellow-white.

Adding more slimline fixtures underneath existing ones because most of the existing fixtures had cooked ballasts and failed lamps and so are not bright enough. Won't it be cheaper to fix up the old fixture than to run new circuits and install new fixtures.

Surface mounting a recessed troffer underneath a overhang and wiring it up with romex. The last time I saw the light it was heavily rusted.

Using F32T8 lamps on F40T12 ballasts which make them flicker badly.     

-I see many HID fixtures using either the wrong HID lamp (either larger/smaller wattage or wrong type - usually MH in a MV fixture, and HPS in an MH pulse-start fixture) or an incandescent lamp in the socket.

-Mismatched lamp colours or T8's in a T12 fixture - all too common.

-When I moved into my house, a nice GE mainlighter was installed with one end not completely in the socket. End was very black. It still works today, though, 10 years later!

-My house also had receptacles wired so the hot & neutral were reversed, and several breakers were double-tapped. I later bought a used power strip that had hot & neutral reversed (it had been "rewired" by Mr. Handy Homeowner to include "noise supression"). I couldn't figure out WHY I kept getting shocked when changing lamps when power was off!

-I always find it interesting when I see an outdoor light that had failed and the handyman installed new wiring and a new fixture below it, leaving the original in place.

-I found outdoor lights at my parents home that had been wired using NM cable underground (which failed) and even lamp "zip" cord (which failed). The latter had a fixture that worked for about 2 years. Years later when I finally got around to trying to fix it, I discovered the wires were all taped together, no wirenuts. It still doesn't work because the light is cemented in the ground with no junction box and the zipcord failed deep under the rockery. I just removed the fixtures & installed solar ones!

-The clubhouse in the same neighborhood had 100w bulbs in 60w-rated fixtures = all sockets/fixtures melted & failed.

-Outdoor lights with photocontrols taped over for "manual" control but switch always left on = dayburning.

For more fun: Visit electrical-contractor.net and look at their "violations" forum. I never cease to be amazed by some DIY wiring jobs.

Yeah mislamping drives me crazy. I usually see HPS and MH mixed together and when you look at it you can obviously see something is wrong. When these people are replacing burned out bulbs cant they read or LOOK at the bulb.

For more fun: Visit electrical-contractor.net and look at their "violations" forum. I never cease to be amazed by some DIY wiring jobs.

Ahh I remember this site, there's also another one called electriciantalk.com that also has a similar violations forum. My personal favourites from electrical-contractor.net is:

I wonder if this is wet location rated :

Original Thread

Err what's this for lighting or a new style satellite dish 

Original thread and more pictures

I think you already posted the second one on L-G but it's just too funny to me and I'm the other members will also agree with me.

I've seen lots of stupid stuff...someone ignoring the notches on the endcaps of an F32T8 lamp, pins arced and torched the whole fixture! Or when an HO ballast failed to the point it was smoking!

Here's a good one. I worked at Home Depot in the elec/lighting dept. One day a guy came in and was rewiring his house. Of course we suggested romex of the appropriate type but he insisted on 18/2 zipcord/lampwire. After several attempts at explaining how stupid and dangerous this was we gave up as he would not budge off the zipcord because it was cheap. So we ended up tossing several smoke detectors in his cart and told him 'okay then you will need these for sure' and sent him on his way. Amazing.

I was just at an abandoned grocery store the other day. The store closed years ago but they open the building on occasion for special events.

The entry way was lit with rows of drop ceiling troffers. They had a mix of every color lamp you could imagine, some lights worked, some did not, some had diffusers, some did not, some just had a tangle of wires hanging out of them.

The main part of the store was lit with 8' slimline fixtures. Most of the lights in the front of the store had T8 lamps but the further back in the store you went more lights had T12s. A few were burned out but most worked. All of the working lights looked good, so I assume they had matched the correct lamps with the correct ballasts (I was a little surprised!). However, the T12s were a mix of colors, ages, and wattages. It looks like they replaced the lamps individually when they went out. They definitely did not replace the lamps in groups.

One slimline light down a hallway was strobing violently. I didn't go down that way to see why. The flickering and flashing was something else. If one of my lights did that, I would turn it off immediately!

-Nelson

How about this?

http://www.youtube.com/watch?v=gWLX8jm_M1g

WOW!  that's crazy! that's a lot of mercury right there....

That's pretty damn stupid. Doesn't fluorescent glass splinter when it breaks and isn't the phosphor coating carcinogenic?