He's going dahn! Never trust a man with short legs, his brains are too close to his bottom. Noël Coward (more interested in the bottom probably)
I just noticed your "he hadn't a leg to stand on" quote, had I only seen that claymore like wit before soiling your eyes with this.
Having short legs has nothing to do with the distance between a person's brain and bottom. Having no neck (Gladstone Small) would offer a semblance of realism to your joke.