Ever have something that was supposed to be a good thing turn out to be a bad thing?
If you're on of those managers who thinks that buying pizza for your underlings is a reward take note, it usually is.
However, it's an awkward form of punishment if you buy the pizza from one of the following places: Pizza Hut, Dominos, Papa John's.
Those pizzas are worse than whatever the people you are trying to reward would have eaten had you not bought crappy pizza for them and had them eat it. If people know that it will be one of those types of pizza, they will find an excuse not to participate in your little pizza party.
If all pizza is the same to you, ask someone who knows pizza what to buy. It won't be as cheap as Pizza Hut, but the people you're trying to reward will genuinely appreciate it.