I have the same issues with being overly competitive with myself. I have occasional rounds when I get a bit mad. I'll give you the same advice a coach (different game) gave me a long time ago. When you throw, stay over your shot, hold the finish, then watch the full flight of the disc. Resist the temptation to walk away, turn away, or do ANYTHING except observe your shot and observe the physical feedback, and if necessary, passively observe the angry thoughts that go through your head.
Besides the observation practice being good for your game, this also distracts you during the time when you would otherwise swear or do whatever tantrum-like behavior we do when we're pissed off. It replaces a negative impulse with a good habit. It helps. It isn't a cure-all and you'll still have issues now and then, but I promise that this helps a LOT.