Waiting in Line

What is it about waiting in a line that makes adults forget some of the basic rules they learned in preschool and kindergarten?
In the morning when I drop my daughters off at preschool, there are always "cutters." Several of us will be waiting patiently to approach the drop off point and then someone will zoom past us, squeeze in as a car is pulling out, drop off their kid and zoom away. It makes me crazy. More often than not, the violator in this case tends to be a man. I'm going to go out on a stereotypical limb here, but this is what I imagine is going through his head: "Holly Homemaker has nothing important to do this morning except go home and eat bon bons. I have to be somewhere. These moms won't care if I zip in front of them." I'm waiting for a case of road rage to happen in the school parking lot. At the end of the school day there are parents who don't want to wait in line so they'll park in the drive through lane and block anyone who is trying to leave. My "favorite" parents are the ones who don't want to be at the back of the line, so they park in the handicapped spots. There are some parents and grandparents who legitimately need those spots, which are often already taken by those who think they're above the rules.
The grocery store is another prime spot for cutting in line. The store I frequent most rarely has more than two lines open when I'm ready to check out. Once those lines are about 10 deep, the managers will decide "Hey, maybe we need to open another lane." If the manager opens the lane, he or she will go over to the next person in line and push their cart over to the newly open lane. But more often than not, the cashier will simply flip on the light and say "I can help whoever is next" and then it's every shopper for herself. It's like a demolition derby with grocery carts. There are no rules as you compete to be the next person in line. I've gotten to the point where I just stay where I am.
Has common courtesy gone out the window? When did we forget the basic rules?