Tip the fucking pizza guy. If you forget, great, but if you just decide not to then fuck you. Unless the pizza is late, you owe the pizza guy a couple of bucks. He counts on that as part of what he makes and you really do owe it to him because, believe it or not, the fucking pizza company isn't really paying him any more than the people who stand around making pizzas and aren't putting miles on their own cars.
You have a problem with that, take it up with the system. Don't be a jackass to the pizza guy just because you're too fucking cheap to pay him what he deserves for getting your pizza out to you in a timely and pleasant manner.