A pretty dumb angel.
One who doesn't know whether there should be a comma between "pretty" and "dumb," or how that would affect the meaning of the phrase.
One who doesn't eat angel food cake to avoid being a cannibal.
One who stands on your shoulder to whisper advice into your ear but faces the wrong way, thus only allowing the devil's message through.
One who would forget where his halo was if it weren't attached.