Louise doesn't understand the principle - you stole Heaven's wine!
I really don't want to pull the "B" card, but I think that because Heaven is isolated a bit she's considered fair game (or "fairer" game) for some things that they'd never consider doing to other HMs. We see this to varying degrees every year...
We do. But Heaven's shtick is that she's forever the outsider, she plays on it big time. Doesn't excuse the others making her the but of most of their pranks though.