In my opinion, the three adjective can be use for something:'un petit café minable''ce jeu vidéo est nul/pourri'and both 'minable' and 'nul' can apply to someone'Ce n'est qu'un minable''Ce mec est trop nul'Par contre, 'pourri' is more for an object:'ce concert est vraiment pourri'You can use 'pourri' for someone only in the context of a bribed/crooked cop (sorry, I can't find the proper adjective):'ce flic est un pourri' or even in verlan:'ce flic est un ripou'I hope I didn't lose you