stop taking things personally

I work at a theme park, won’t say which one, and everyday, I get those guests that ask stupid questions, get mad when I want to check their child’s height just to make sure he/she is tall enough, say horrible things to me if the child is too short to ride, and disobey the rules – which I get in trouble for if guests don’t follow it. Why do they get mad when I do safety procedures as I was trained to do? Why do they get mad when the child is too short to ride and tell me I’m ruining their vacation? STUPID!