I read this story a few years ago on another forum somewhere, similar situation to yours. Karma does come back on people.
There was some asshole like that ready to go through everything, and he'd been bragging about it, telling people he was going to lock them up. Well, one of his former friends that he was being an ass to found out when he was going to be drug tested. The day before or two days before, they threw him a party at a motel in celebration because, it will be cool to have a cop for a friend and neighbor.
They made sure he got passed out skunk drunk, and for his safety took him in the bathroom and laid him on the floor.
Some potheads crashed the party, and one of them went in the bathroom and lit up a joint. Not only that, but when someone else went to check on their buddy the pothead got scared an ran out, accidentally dropping the roach on the floor right next to the wanna be cop's hand.
They didn't realize it was there , and wouldn't have except a drunk chick decided to go to the bathroom to take some selfies, and got a couple with her and him in it with the joint visible.
The guy, unfortunately pissed hot, lost his chance, and the girl of course as girls will do, posted it on facebook or something and everybody saw it.
The guy never was able to join up again after that. Probably for the best though, because he was a dick.
Karma.