I know where you're coming from, because it gets pretty exciting when you're winning against someone OTB, especially if you know that they're generally better than you. I've never played an OTB tournament myself, but I occasionally play the best guy in my local club and I might win 1 out of 5 times, but that one time makes me want to smile in the middle of the game.
I would try to follow
@White_Queen_1990's advice, just put yourself in their shoes and try to imagine how they would feel if they were watching you try and control your laughter. Respect for the person you're playing should always be present, no matter the result of the game.