Originally Posted by Tera

It could be anything, I had the same problem with my cat for a little while. I had to ask my vet

Either the litter box was too dirty, or you changed litter brands on him, or you moved a blanket or something that has previously always been in the same place. Cats are wierd and can be very habitual.

My cat never seemed finiky or anything and was pretty mellow and welcomed change, but man if his litter is changed (brands) or it's not cleaned enough he'll piss on my clothes. And by cleaned enough I mean I have to scoop it every day at the same time or he gets pissed.

Stupid Cat.