Why tolerate rudeness?

After shopping at my local Wal-Mart and KMart, I have encountered two situations of rudeness. Two weeks ago, I was waiting to use the digital photo machine at Wal-Mart (A machine I use quite often as I am my school's yearbook advisor). After taking his sweet time, I kindly asked the man using the machine if he was going to be much longer. I expected a simple "yes, give me a few minutes." What I got was "I will be done when I am done. And you need to back up out of my space." Needless to say, I was shocked. But, for those who know me, I do not back down to rude people. I told him to change the tone of his voice and explained that I was doing nothing wrong by waiting "in line" to use the machine. After roughly two minutes of this crap, I found store security and explained the situation. I have not been back to use that photo machine since. Today, while shopping at my KMart, I overheard a female customer being very rude to a nice salesgirl. This girl was the only employee working several departments and was doing her best to do her job. I told the customer to not talk to the employee in the manner in which was taking place. The rude customer began yelling at me. I also passed on this incident of rudeness to store management. I guess I should not but into other people's situations, however, I am to the point where I am plain sick and tired of people and their ignorance. As I teach my students on a regular basis, rudeness should not be tolerated from or by anyone.