Breathe. Honestly if you can just remind yourself to breathe deeply and consistently whenever you feel yourself stressing out or becoming impatient you'll find you are much more able to put things into perspectiv. If you find yourself conistently impatient around a particular person then you are not the only one at fault here. Chances are they feel the same way about you and if it's a personal relationship then you should confront them calmly about it the next time you find yourself stressed.
Impatience can be borne from either a too high opinion of ourselves or our insecurities.
If we have a high opinion of ourselves - learn not to judge others. We are all unique individuals with a myriad of skills and experiences. Add to that our quirks and foibles, our quest for improvement and our fallibility; a veritable melting pot of qualities. Celebrate the individual and reap the rewards.
If insecure, we have to work on our confidence and self-esteem. We can't afford to beat ourselves up; have confidence in what we can do and be honest about what we can't. Seek out honest solutions.
Every time you find yourself held up or waiting for something choose to see it as being given an opportunity for some reflective time for yourself. Look around you 'till you see something that enhances your day and that you can be grateful for - maybe just the blue sky or someone less fortunate than yourself. Or if you're in your car and it's raining, just be grateful that you're warm and dry!