It isn't all that easy to piss me off, but once in a while it happens.
This time around I made up a rhyme to calm me down:

Rest thy mind.
Stay thy hand.
Let the hate
turn to fate.

It actually works. More so if you believe in karma or read something like this:
Do not repay anyone evil for evil. Be careful to do what is right in the eyes of everybody. If it is possible, as far as it depends on you, live at peace with everyone. Do not take revenge, my friends, but leave room for God's wrath, for it is written: "It is mine to avenge; I will repay," says the Lord. On the contrary: If your enemy is hungry, feed him; if he is thirsty, give him something to drink. In doing this, you will heap burning coals on his head. Do not be overcome by evil, but overcome evil with good.
—Romans 12:17-21, NIV