I don't get this either.  My only guess is that they are huge and used to lying about how many people they are buying food for.  It reminds me of people who go through a fast food drive thru and order 3 meals with drinks to make it look like they are buying for a family instead of ordering a bunch of food with one drink. But yeah, why be embarrassed about a free pizza?  That just means you have food for the next few days.