Indeed. Super perfect characters/Mary Sues are not just annoying, but a pain in the ass to deal with. If a Mary Sue/Gary Stu get's accepted by the GM for some incomprehensible reason, I often try to rally the other player's together and take out the Sue (or at least weaken him or her severely). But my attempts are almost always in vain; we all start infighting and get shredded by the Mary Sue republic with relative ease, even when we hold all the advantages! Bloody hell. 

I do have a gripe with character assassinations and bastardizations in not just roleplay, but in fanfiction in general. Kakashi isn't a asshole who favors Sasuke, Celestia isn't a evil Despot that lobotomized Derpy, and the cast of Harry Potter aren't 'Goffs.' If you want to show a character in a negative light, say having Harry disliking Ron, then why not have Harry apart of a different house? Have Harry see the more negative aspects to Ron's personality as he was raised differently, instead of having Ron 'go Death Eater' right out of frikkin nowhere. 

One more; I'm a bit tired of everyone playing Ultra Liberal Activists straight out of the 1969 (not that there's anything wrong with Woodstock :p). This isn't something pertaining to my personal beliefs; this is more similar to a trend growing stale. That, and I'm not a fan of 'fixing' settings just to fit the RPer's political, religious, or sociological beliefs. Especially when it gets the point where they actively demonize characters and then have their characters start ranting for no reason. This also applies to fanfiction, but I can understand why some people would enjoying playing that character.