Yeah, the whole stamp pretty much explains it. I honestly don't give a shit if a certain character I like is a Mary Sue or a Gary Stu.
And the truth is that I actually sometimes find Mary Sues to be likeable, like Flash Sentry and Fluttershy from MLP: FIM
However, when it comes OC's, I can agree that people do overuse and give their characters cliched backstories and traits, but I wouldn't immediately call them a flat-out Mary Sue.
Seriously, some people treat characters with no flaws or too many flaws or whatever traits they have that defines them as a "Mary Sue" like they shouldn't exist at all.
stamp template (c) ~Wingless-Butterfly55