The Unreturned High-Five

Listen here, you magnificent moron, you tried to high-five a *tree*. Trees don't have hands, they have branches, you walnut. This 'joke' is funny because it's a play on words. 'Left me hanging' means both literally that the tree didn't reciprocate the high five and figuratively that the person was 'left hanging' or disappointed and alone. Maybe you should try talking to a person instead of a plant next time. Just a thought.