Not all hotels come with the luxury of a microwave, so when you're in a room with your friends, order a pizza, pass out from booze, wake up and crave some of that leftover pizza, you don't really have any heating options.
That is unless you're an extremely efficient individual, and McGuyver yourself a stove using only a clothes iron and a hair dryer.
It seems like a fool proof plan as the iron heats up the crust and the hair dryer has the toppings covered. It's almost as if the iron was made for pizza slices with its similar shape and size.
Sure, only God knows what disgusting things live on the surface of that iron, but by this time, you should be buzzed enough to not worry about that.
If all else fails, cold pizza is just as good as warm pizza -- Because it's still pizza.