Worst thing in the office place was when some idiot left their window open in the middle of Winter, temps fell below 0F with high winds, and froze the 2" sprinkler pipes running over their office. Flooded most of the 2nd floor then started running through and raining out onto the 1st floor (and then into the basement). And it happened during covid lock-downs so it was fortunate anyone was even in the building to report it.

My own personal oopsie was checking network cabling in a small room, bent over to check things low and then wandered out to check elsewhere... Then noticed there was a LOT of commotion on the sales floor. Turns out I hit the power switch on one of the phone cabinets with my ass and shut down half the phone lines.