There isn't a lot of showing off here, to be honest. The back spin dribble is common before a free throw; a lot of players use it to focus and get into rythm. Unless he threw it unreasonably far, it's not really showing off. Even if he did throw it unreasonably far; give it back to him.
If you want to make a point to him, just smile and shake your head while you give it back.
