I accidentally bumped into a midget yesterday.
Me: "Are you ok sir?"
Midget: "Well, I'm not happy."
Me: "Well, which one are ya?"
Listen up, buttercup. The joke plays on the word "Happy". The person who bumped into the little dude asks if he's okay, and the midget replies that he's not "happy". Then, the first person asks which of the Seven Dwarfs he is, you know, from Snow White. The joke is kinda dumb, just like you.