"Unrealistic boobs" is just one of many variations on "I like a different brand of hot sauce". Happens a lot in art. Clearly, you like 'em that way. Which means that criticism can't touch you, assuming you're making this for yourself. (If you were selling it, it'd be a different story of course.) On the other hand, if you do like praise from others, it's good to have that kinda feedback. Hopefully, the people who like it just the way it is are saying so, too.
My point - to tie this all back to the original question - is that it's kinda hard to get truly bad criticism, but the worst for me (assuming I ever get around to making my own) would be criticism that didn't have much thought behind it, on art you put a great deal of thought into.