Living in a big city or even small means having to deal with a lot of people some of which can be a little bit rude from time to time or can really take out the worst in you, making staying calm a lot more difficult than it should be.
Or sometimes you just wake up in a bad mood, you had a bad night, you have a lot to do, there's not enough time and you feel like your life is going to come crumbling down if you don't get everything done by the end of the day, when in reality it won't.
It doesn't matter the reason, what matters is that you don't lose your cool and your patience just because something is going wrong, so today count to ten and back if needed, but don't take anger or annoyance out on anyone, they don't deserve it.
Try something else, punch something, pinch yourself, eat something, drink some water, calm yourself up and keep going with your day. Just because you are in a bad mood doesn't mean the world around you has to be too.

“Speak when you are angry and you will make the best speech you will ever regret.” 

Ambrose Bierce