give (one) what's coming (to one)

To give someone that which they deserve, which can be a reward or retribution, depending on the situation. Don't worry about those stool pigeons, we'll be sure to give them what's coming. After all her hard work, I really hope the company finally gives Mary what's coming to her. You've repeatedly come to work late despite warnings, so, yeah, the boss is gonna give you what's coming.