To complain about something that you paid or will pay for. A service for example (at a bar, restaurant, hairdresser, Flight etc)
After complaint you got a form of compensation (free drinks, discount etc.) and then you brag about to other people how successful you where. then you Nag 'n brag
«Dude i got this drink for free, because I spotted some lipstick on my glass, I got skillz» «You are totally Nag 'n bragin»