What's green and has wheels?
Grass, I was just lying about the wheels.
Green With Wheels
Explanation
Explain Bear
Listen up, nimrod. The joke sets you up to think of somethin' green with wheels, like a lawnmower or somethin'. But then BAM! It's grass, which ain't got no wheels. It's funny 'cause it's unexpected, and you ain't smart enough to see it comin'.