My mindset is "I'm going to be very careful, shoot every shot as perfectly as I can, never settle, always line up the shot first, and basically make sure every single shot is given serious treatment. If I miss or screw up, I have zero reasons to be mad because I gave the shot 100% effort."
The hard part is remembering to stay that way the entire tournament. You get lazy and start to skip steps on some of the routine shots. It's exhausting a little, mentally, to give maximum try to every ball. But that's what you have to do. Then you have no excuses and no recriminations afterwards.
If for some reason you get mad anyway (it'd be completely irrational) never let the opponent see it. It pumps them up and hurts your game to fall into any sort of negative thinking. A big part of winning is to get in your opponent's head a bit. Don't ever directly shark them, be classy. But allow yourself to be intimidating. If you have a 'local hero' reputation, play it up. If not, just remember to never let 'em see you sweat. Treat every bad roll as if it's a minor inconvenience on the way to your inevitable win, and just grin and do your level best to deal with it. Also grin if you get one of the good rolls.
If you really want to mess with them, act very casual after every amazing shot, like it's routine. Don't laugh and squeal like a little girl. Also don't joke around with the opponent. If they come to you looking for a little fellow-pool-player sympathy about a tough roll, give them nothing. "haha, I was trying to bump the seven and the 9, what are the odds I'd go right between them and scratch?"... you can just kind of smirk and shrug like "uh huh." Come off a little cold, it makes them uncomfortable. If you are the one looking for sympathy... stop, it's a sign of weakness

...also this is maybe less than classy but if they have an angry outburst, you might allow a little smile to show.
You may already be done with this tournament, hope you did well if so.