One of my biggest ones is people complaining about 'non-creative characters'.
People express their originality and ideas in their own way, and everyone has different views of what makes a good design.
Just because a design isn't up to 'your standards' or there aren't enough of a certain species doesn't mean you should go around insulting the general public about it, and it's rude to say especially since you don't know the story or ideas behind the design itself.
This isn't a callout to anyone specific, I've just had a lot of people insult my characters over the years for not seeming to be creative enough, which I find quite dumb.