I don't think it's intended to mock the artist, just anime culture in general. And for that matter, I don't think anyone is really mocking it, it's more playful joking. It's hard to find a group of people discussing anything on an internet forum (i.e. nerds) that's not full of current or past anime fans. And even there, I'm not saying nerds to try and actively upset anyone. It's just a joke, and part of the age old tradition of co-opting terms that could be or once were used as insults and making them your own in order to take the legs out from under them. In the whole world of fandom, most 'insulting' terms are probably going to be jokes. When you get right down to it, none of us have the right to look down on anyone.
Edit: It was a joke please stop hitting me
I'd rather have him speak for himself. I'm referring to the comment
"Why is the 3rd ones head animu style, and the other two have tiny heads."
and not the later discussions about anime.
Even if you take the term "Animu" as a joke - what's being made fun of? The laughter is at the expense of the artist or at the anime culture. I could go more in-depth onto why it's a retarded thing to say (is Archie anime? That and golden age comics with exaggerated proportions have been around longer than the entire history of animation in Japan.), but that's besides the point. The comment was at best a malicious attempt at being facetious.
There's petty criticism and there's constructive or supportive criticism. The difference is often a matter of attitude. When giving criticism to someone else's work, I believe there's a modicum of responsibility that you have to shoulder.
Edit: I know it's a very sensitive topic around me because I believe it's innately wrong to solicit your own criticism unless you're friends with the artist, it's asked for, or you express it tactfully. You can speak personally and say "This is what I like" - but for me, that above comment is tantamount to saying "Your art sucks" (and providing no useful detail whatsoever). It hurts, especially on a professional level.
This is why I prefer the modding culture, because the only person you're obliged to satisfy is yourself (and maybe the people you care about). If you have gripes with someone's art, mod the art yourself for yourself. (Of course, this is harder to apply on the professional level, which is why I find that criticism painful.)