I just think it looks like the same style of art you'd see in beavis and butthead or something. If he doesn't mind, then more power to him! I don't think anyone here will care that much.
There's nothing in the MM against it that I saw- but does he realize that if he uses that avatar people will think of him as "That one dumba@@ in the shower"?
The whole point of avatars is to represent yourself online, and most people won't get the snarky, it'll just be a dorky picture.