Proper to laugh at a coach

[Hornets222003]

Last week, I was officiating an AAU tournament. A player drives to the basket and gets his shot blocked by a player that outweighed him by more than 50 pounds. The player jumps straight up and blocks the shot, but the offensive player runs into the defensive player. The contact - which I ruled incidental - caused the player to go to the floor. He curses in my direction and I call a technical foul for the language.

Later in the game, the coach calls me over and says that his kid says that he didn't curse. I started laughing and walked away. I had no explanation. Laughing was all I could do. The kid cursed. I was standing right next to him. There are only so many words that sound like "duck." Is laughing at a comment from a coach ever ok?