It's rude to stretch your arm out in someone's face.
Hal is watching a movie at a theater with people from school, Linda and Lynn are on either side of Hal and Joe is beside Linda, Joe's girlfriend.
Hal's shoulders start to cramp, and he wants to stretch his arms out.
Hal announces that he has to stretch then carefully squirms so as  not to hit  anyone.
Hal thoughtlessly stretches and hits Linda in the mouth.
Hal feels much better and no one was hurt.
Linda cries and Joe punches Hal.