Willie: I'm an eating, drinking, shitting, fucking Santa Claus.
Willy:...and I went to my father. And you know what he did? He kicked my ass. And do you know why?
Kid: Because you went to the bathroom on mommy's dishes?
Willy: Were you dropped on your head?
Kid: My head?
Willy: Of course your head. Who else's head are we talking about?
Kid: How can I be dropped on my own head?
Answer: My guess is that when he was a child, he was molested by a man dressed as Santa Claus, and ever since then he has been holding a grudge against people dressed as Santa Claus. You can see him staring angrily at Willie in the bar even before Willie notices him.