People who act like that end up on my shitlist. Basically if you can't show human decency then I don't care about you, you are a piece of shit and I'll do my best to carefully and slowly let others realize what a shitdick you are, I won't be honest to you unless being honest just so happens to serve my agenda, and while I wont burn your house down, I'll gladly watch it go without lifting a finger to help put out the flames.
That's what happened at my last job, and I'm fairly sure whoever got it after me will be better off because of it. Had to work under an idiot cunt istj but now everyone knows he is a cunt and he wont ever be able to boss people again. For example the motherfucker wanted me to work extra by going around and putting advertisements in peoples mailboxes, after I did this the first time he said he didn't want "to be ruined" and cut the measly payment in half. I expected measly payment from the cheap son of a bitch, but not to have it cut in half. I also knew that if I confronted him and said "this is not acceptable" I'd be the one to suffer for it. So I just threw half of the advertisements away instead of putting them in mailboxes and then I told my actual employer with whom I had a good relationship about how this ISTJ decided to cut my payment in half like that without warning, of course I left out the part where I threw away half of the advertisements so that the focus would be on him being a total fucking douche and not me cleverly douching him back without him knowing it. And of course I didn't say it in an angry manner, but rather in a naive baffled and somewhat disappointed manner. That way it really seemed like he was taking advantage of me.
Then I might say something nice but totally trivial about him at some other point, something that is positive but really minor, just to make it not seem like I am out to get the guy. Then the next time I might say something that makes it seem likely that the ISTJ dick has done something shity, but I won't say that he has, I'll just appear a little stressed out, like he's been on my ass. That way I'll get asked "Hey is xxxxxx making you do this again?" and then I can look away and down for a little bit before looking back up and admitting that he has. that way it seems like I'm reluctant to trash talk even when its warranted. All the while it will give a lot of weight to what I say, a lot more than if the recipient had qualified it as trash-talking. It is very important not to appear like you are victimizing yourself or like you have it in for whomever you are trying to undermine. It is also important to let this take all the time it needs, even if you veil complaints you have to let there be space between them.
I am really glad that I am able to do this, I think INTPs might want to consider using similar tactics. Note that such tactics should be reserved for true douchebags however. Otherwise Redbarons approach is the best.