In Taming the Tiger Within by Thich Nhat Hanh, he suggests the following:
When anger comes up, take out a mirror and look at yourself. When you are angry, you are not very beautiful, you are not presentable. Hundreds of muscles on your face become very tense. Your face looks like a bomb ready to explode.I took Hanh's advice. I bought a small metal pocket mirror I keep in my back pocket. It's been there for about a month and a half. Never had to take it out--yet. Just having the mirror there reminds me not to get ticked off.
Now that's practical mindfulness!