Not doing the dishes when it's your turn. FOR THE LOVE OF GOD, I HATE A DIRTY SINK. D: Or, letting the dishes pile up (and not notifying me) because their mother came over and did them beforehand which apparently means that was her "turn". How lazy! Now I just wash my own.

I like things to be tidy, so having the room/house look like a bomb just hit it is NOT a good way to go.

Change the toilet roll if you've finished the last bit! And yeah, definitely don't let the toilet paper run out. Had that one before, too. >:c

If someone goes away for the weekend, and your roommate watches your pet, keep an eye on it! My roommate let my rabbit out of his cage once for a run around the backyard. He escaped under the gate and ran for the hills, and I was only told about this when I got back. She knew my rabbit was like Houdini, why would you let him out and then not watch him?! She did find him eventually, though. Said she went around knocking on the neighbour's doors to locate him. Also, he ate my entire Jasmine plant. </3

I have many more, but tidiness and cleanliness are my big ones. xD