I was so angry too when some drivers who had no manners were cutting off my line. But upon entrance, while the security guard pass me the ticket, he said "very good morning to you sir!"
I was so shock at that time with this guy's politeness. He just smile at me and all of sudden, my anger just drop off and I smile. Suddenly with that greeting my day was brighten up. I never thought that a simple polite greeting can really change our mood. So don't underestimate it.