People who can't help but firehose the toilet seat, rim, wall, floor etc. and then don't try to clean up.
Right, on that note, story time.
I was a maintenance plumber at a very well known investment firm, and we had one toilet which would block and when we went to unblock it, the walls, seat, everything would be covered in dung. It got to the point where we'd actually started to monitor the toilet to see who the culprit was. Turned out it was a lady of the Muslim religion which explained it all, as her religion dictates that she would have to face a certain direction when curling one out and toilet paper is obviously a nono. We hung up notices to attempt to curb her rather enthusiastic doodoo manufacturing process, all to no avail, it just carried on and on.
Behind the toilets was a void for maintenance purposes, which contained the cisterns, chemical dosing systems, etc. Eventually a colleague and myself went all childish and he hid in the void. We had our radios on us so we could talk to each other and I waited in the lobby pretending to fix a not-broken light fitting. Eventually the dump truck came in so I waited until she got all comfy and when I was sure that maximum comfort was achieved, I signalled my colleague who flushed the toilet from behind.
She came out screaming with her legs covered in pee, pee all over the floor, holding her dress up, in to the middle of the office where the dealers sat.
It was an amusing day, that toilet was never filthy again.