Why are people such jerks?

I ask myself this a lot. More often when I'm at work. What makes one person feel the need to be rude to another? I used to run into this a ton when I worked at a big box pet store. I had one lady shove a cart at me because she was pissed that we were out of her dog food. Today a woman complained with big angry drama at me because she had to wait so long. I am but one person. I can only move so fast. I was doing all I could not to take her glasses from her, crush them into tiny pieces and tell her that maybe at the next place she wanted them fixed at, they wouldn't take nearly so long. The anger just stayed with me for the next hour or so that I was there. I can see how the jerk-ness can just travel around. I was doing my best not to let it seep into other areas of my day but everyone just kept pissing me off after that. I left work and headed for the only remedy that I'm aware of. Puppies. Yes, you heard me. I went home, let the dogs out and just ran around and played with them for a half hour out in the sunshine. And when I came inside, I made chocolate chip cookies. Real ones. Not the diabetic crappy ones I made the other day for the sake of my parents (sorry mom, but they ARE truly nasty) but the REAL ones. I ate cookies and took a catnap with a REAL cat and by george, I felt pretty good after that. So here is my proposition for world peace. Send everyone a puppy, some sunshine, and some real-ass chocolate chip cookies. The world would be a better place.