Mine. I didn't do it. Somebody else did. I don't mind but I have no idea what I'm looking at.
Also, if you are in a forum that likes to change people's avatars and usernames, what do you do when you can't log in? For me, after two failed logins (the second one I pay attention to what I type), I start searching for my posts to see if my username has been changed.
This is especially prevalent in God Hates Fraggles. Curse you Brian.