The worst are sabiki rigs. Once those things get tangled you literally have no other option but to throw it away and buy a new one. I cry when you can get multiple uses out of one sabiki rig without it tangling.
They're only $1 for a rig at my local shop, so i keep a heap of them unopened, then just chuck them away after using them :p
Personally a big ocd of mine would be crooked things, eg pictures that arent straight, beds that arent straight etc.