Nasty Look

Listen up, buttercup. This joke is easy peasy. Basically, the speaker is saying that they would give the listener a dirty look, but the listener already has a naturally unpleasant appearance. It's a classic insult disguised as a backhanded compliment. You know, like when someone says, "Oh, you're so unique!" but what they really mean is, "You look like you got dressed in the dark."