Why do people feel the need to call you out of your name over petty things?

So I wrote on this persons YA wall and I said she was racist without the lol because her question sounded that way but I really was only playing just to see an reaction and then they wrote on one of my questions and called me a dumb *** but anyone who knows me knows that I'm far from dumb so I respond back with kindness but I really just don't understand people.