This is a reference to this scene, it's called sarcasm
She told the pizza dude she knows that he always stared at her in school. Embarrassing moment for pizza face so he stated that he always looked at the clock behind her. In the pool scene she wears her b*tch bikini in front of the clock and asks him "Are you looking at me ... or the clock?"
This whole movie is about this sexy clock, no one cares for the girl!
You should rewatch this masterpiece a few more times to spot all those details!
I guess most people miss those tiny things 'cause they are drunk while watching it.