Having a 2 people added to a blacklist is fine. I've done far worse things to my career.
edit: ok, you don't need to be as rude as I am, but I'm a known asshole, so ymmv.
When I called the other company, they asked me to sign with them even though I'd already signed a different offer. Because this is tech and people do it all the time.
It just felt dirty. I had already made my choice, and would not have changed my mind. But I've got an older mentality where it feels like I am burning bridges if I reneg after signing an offer.
It's one thing if someone says they are debating between a couple offers (as you did); at that point I'll fight hard for the candidate that I want. But the instant someone commits to an offer somewhere else they're entirely off limits and I wouldn't ever counter-offer at that point even if they would take it.
If you ask, they say no, and then you reneg on the offer, it's kinda shitty but somewhat understandable. If you don't ask about the exploding offer in the first place, that's 100% you being a passive-agressive dick.
The exploding offer is a psychological manipulation designed to give the company leverage in negotiations, how is that not passive-aggressive?