How about the 3e version of the shedu. I mean, shedu aren't that silly by themselves. But the author of the conversion decided to give it a fifth leg in honor of a stylistic technique used by the Sumerians to convey depth. That's a bit silly.
Another monster I have a problem with are boggles. Blue monkey-goblins that can reach through dimensional portals? Not too sane there, and I've never been able to treat them remotely seriously after a group I DMed suggested that they should say only their name, as if they were Pokemon.
Demiurge out.