Some diet plans incorporate a 'cheat meal' or even a whole cheat day. However, they work best when dieters eating normal portions of foods they don't usually eat, instead of eating to excess. Maybe limit yourself to one or two slices of pizza, and fill up with salad?
They say that it's what you do across 7 days that counts, not just one. With that in mind, a lot of people eat a little less during the week and bank their calories to use on weekends. That might be an option.
In the end, it's really trial and error and what works best for you as an individual. If you splurge on weekends and still see an overall loss over the course of the week, then you are doing fine. If not, then it's time to tweak your splurges