Shake hands after you lose the round. People trust the ones who lose well.

Losing badly is easy and it is also the most public thing you ever do. The moment after a result is the moment you have the least control, which is why people read it so closely; they are seeing you with the performance stripped off. Someone who can be gracious while disappointed is telling the room that their behaviour is not controlled by outcomes. That is exactly the person others want to depend on later.

Decide your losing routine before you need it. Hand out, eye contact, one sentence, no excuses about the officiating. Then be as annoyed as you like afterwards, privately, where it belongs.