Paul Fairhurst asks Mark Crossfield in this Q&A "When I play a couple of my playing partners get really down on their game and silence follows, it really throws me off! what can I do?"
Mark sees this so often and discusses how he only plays for fun and tries to make light of how serious people can get and how grumpy people are. Find people that enjoy playing the game like you do. A more extreme thing to do could be to film them and show them how silly they look when they throw a tantrum. This works!