How can you 'break' an iPhone charger without being noticeable l?

There is no safe way to do it without risking the charger ruining the next phone it's plugged into nor without risking the charger going "BANG!" and possibly causing a fire next it's plugged in.

I see no legitimate reason for you to do as you ask: if it's for a prank then there are no jokes when it comes to any device plugged into main AC outlets.

This is WRONG. I do not think anyone here is going to help you, because clearly you are up to something not nice.