Haven't killed anyone yet

Why are people stupid? Why do people start things, be extremely nit picky, then back down and act like it was nothing and it doesn't bother them? It pisses me off more than when someone is actually mad at me, at least I know whats going on then. 
Time and time again, people have to be personally offended, but yet they can say what they want. Hypocritical assholes. All I can think of some days are taking someones head and slamming it into the wall repeatedly until they shut up. 
And people ask me why I don't want to work customer service.