You shouldn't pull someone's hair.
Jack is hanging out with some friends, and they are all telling jokes and goofing off.
Jack wants to get his friends to laugh.
Jack tells a funny anecdote about pulling hair instead of actually pulling hair.
Jack pulls his friends hair hard to try to get a laugh from the others.
Everyone has a laugh and enjoys Jack's story and everyone has a good time.
The friend is hurt and everyone is wondering why Jack did that because it is not funny.