You shouldn't get mad at someone who is helping you.
Danny is helping John paint his apartment and John notices that Danny is painting the wrong part of the wall.
John wants to tell Danny to stop painting.
John doesn't tell Danny he's doing anything wrong, he just simply tells Danny to take a break while he finishes the wall.
John yells at Danny to stop, calls him an idiot and exasperatedly tells him he's doing it all wrong.
Danny is happy to take a break and thinks his friend is giving him a break because he appreciates his hard work so far.
Danny is stunned that his friend is so mad and is offended that his help is being criticized.