I've never seen an anchovy, I've never known anyone to order anchovies on his pizza, and of all the pizza restaurants I've eaten at, I've only seen anchovies offered as a topping once. Yet, in every movie where pizza is mentioned, somebody has to request anchovies.
Well, guess what, Hollywood. It's not funny.
Just like the obligatory crotch-kicking scene, I loose a bit of respect for whatever movie that over-used "joke" appears in.