Next time you're on hold or sitting in traffic, time how long you actually wait. Chances are it'll be much less than it feels. Then ask yourself: What difference will an extra five to 10 minutes make in my day, anyway? Probably not a lot.
Interrupt the fight-or-flight response
The minute you feel yourself getting impatient, stop the release of cortisol by paying attention to your body. First, breathe deeply. Then roll your shoulders (which are probably near your ears by now) forward, up and back. Repeat. This interrupts your body's negative physical reaction so the blood flow can go back to your brain and you can think more rationally.
Turn a "problem" into an opportunity
Caught in traffic with nowhere to go? Use that time to play a book on tape. Stuck waiting for an elevator? Get your daily exercise by climbing the stairs.
Follow the golden rule
The next time you want to honk at a driver who's driving slowly or yell at an airline agent because your flight is late, ask yourself this: If I were in that person's shoes and doing the best I could under the circumstance, how would I want to be treated? Extend grace, and it will always come back to you.