Is there any aspect of personality of Mary Sue that you expect readers will find unlikable? 

Yes

Kitty is a kid. She has a bad mouth, a bad attitude, and sometimes shows her bossiness to other kids. She has a "me! Me! Me!" attitude and is a 7-year-old narcissist. She even makes MY blood boil when I write her! God I hate her.

No.

"Being unlikeable" and "having flaws" are different. Granted, being unlikeable isa flaw, but this question specifically asks if the character is unlikeable to the reader,or has unlikeable traits to the reader, not if they have character flaws, which does not automatically make them unlikeable. I suggest changing the wording of this question.

Yes.

A character without personality flaws is probably two-dimensionally perfect, like Superman.