It's rude to have fun at someone else's expense.
Tim is at the playground with his friends when he sees someone trip and fall down.
Tim wants to react to the person tripping and falling.
Tim goes over to the person who fell and helps them up.
Tim imitates the person falling in a comedic way getting a laugh from his friends.
The person who fell feels like Tim cares about their well-being.
The person who fell feels silly and embarrassed at being the butt of a joke.