I tried to change my avatar to what I think of is a cool looking spruce stump I dug out by hand. Instead I get a bright green avatar that irritates the crap out of me. I tried to delete my account and can't even do that.
As for deleting... most forums won't allow you to do that unfortunately. I used to tell people who wanted to delete their account- change the password to something you'll probably forget then delete the bookmark.
In really extreme cases I would think account deletion would be the way to go. Or merge with a new account (have had to do that...not fun).