Does Happy Tree Friends really count considering it's more of a web animation than a regular cartoon? I know that it aired on television for a short time, but I wouldn't put it in the same vein as other cartoons.
Not to mention, as others have mentioned, I'm pretty sure the song is supposed to be annoying. Literally the whole show is supposed to be a twisted satire of cutesy preschool cartoons, so having a theme song that reflects that makes sense. He can hate the tune all he wants, but given that it was purposely annoying, it isn't worth getting worked up over.