LOL for me I never truly grasped the term 'mary sue' since like you said, people seem to like to alter the definition of it to justify their irrational dislike for a character at times. I can understand the basic idea behind it and I can laugh at really bad ones but it's one of those things that can be overused. I also feel like there are better ways to explain why you don't care for a character if you feel she is too weak or you don't agree with her actions. But I also fear that people just like to dislike a female character simply because she exists. Some characters I feel are unbelievable in that they are too 'perfect', but in a sense for a female to be a captivating heroine, I feel that she needs to possess some kind of special reason to grab people's attention and to root for her. But I dunno, again, I never use the term since I never fully understood how/why people use it XD