"I'm afraid I can't see the problem with the "little moron" jokes: they can, surely, only be seen as slurs against the intellectually deficient by joyless humourless oafs with no imagination. They're merely puns on the word moron."

Well I suppose you could think up punning jokes about "little Nigger" or "little Yid" too if you set your mind to it. But I wouldn't advise it.