Had a few over the years.
One tightass client had their server rack set up inside a shower cubicle, with tiles, plumbing etc still in place. They had installed a splitty AC up on the wall to keep things cool. Problem was, the server rack was mounted sideways, so unracking servers was impossible once the rack was slid into place.
It all worked, but was sooo dodgy. No UPS, around 3 switches between one room and another etc.
Another site had a splitty up on the wall with racks directly below it, Condensation drain outside blocked up, so it dripped all over the racks and took a $500mil org offline for a day or two until replacement kit could be sourced.
Another site had the chillers fail/trip off for their server room, it hit around 60-65C on the door handle to the room, according to the fireys who fired an infrared thermometer at the handle. Big red switch was pushed. PDUs have since had temperature monitors installed, and high temp cutouts enabled. AC is still woeful though, with AC coming from the ducts in the ceiling, and no way for the hot air to get out, other than rising to some return vents.