If you hate people, why must you tell everyone about it?

So I'm riding my bike this morning in 16 °F and first a jeep passes with a spare tire cover that says, "I hate people." Then when I get to a local Target store I see someone is wearing a sweatshirt that says on the back, "Go to Hell." These are both expressions of hatred. I don't get it. Has it become hip to hate people? If you hate people, why must you tell everyone about it?

Now if I had seen "I hate stupid people" posted on someone's car or the back of a shirt, I might agree with them but still I wouldn't be broadcasting it.