TL;DR at the bottom.

A bit of background; so up until a couple of months ago I worked with this guy, let's call him Tony. He's the kind of guy who everyone loves, but is actually a bit of an dick, however people tend to look past it because he is energetic and funny. We both worked in a pretty tight environment with a team of 8 other people. We worked long periods (almost 3 months) full on, then had a good chunk of time to relax, however we were still working together during these periods. We often used this down time to blow off steam by going out drinking and meeting new people, hooking up, etc, stuff we couldn't do during our 'on' time. 

So I'd been working with Tony for about a month in an 'off' period, and we'd got on really well. He was a pretty intense guy, a heavy drinker, and when he was drunk he would get pretty loose, not really having a filter, saying whatever he wanted, not really caring what happened or who he hurt. It was pretty funny, because we got on well and I was never on the recieving end, and it was mostly harmless. Then one night just before we start our 'on' period, we go for a night out. I'm late to the party, so I'm more sober than everyone else, but still up for a good time. I meet them at a bar, and the first thing Tony does is smack me in the balls, in a friendly way, but hard, I'm pissed off, I tell him to fuck off, he argues with me but eventually does. Not wanting to ruin a good night, I tell him to come back in 5 mins when I've had a chance to cool down and forget about it. 5 mins later he comes back, and we're all cool, albeit a little tense. We move on, keep drinking, and eventually, after a few bars, decide to get some food. I'm still relatively sober at this point. During the process of getting a hotdog, an argument breaks out between Tony and some locals. I do my best to intervene, trying to calm down this other guy, while our coworker tried to calm down Tony. Suddenly Tony turns on me, pushing me, telling me not to get involved, telling me not to get in-between him, etc, luckily nothing physical but pretty intense stuff. Eventually I tell him to go fuck himself, and walk home by myself. The next day it's put down to a drunken argument and we move on. However this starts an air of tension between us.

So then comes our 'on' period. It's a pretty high stress time, however the 10 of us are a strong team so we get through it. However Tony is turning into a bit of a dick to me, it starts with "jokes" than are a little personal, then turn into him slagging me off to the rest of the team behind my back, although within earshot. I confront him, we move on, and again it kinda gets forgotten about, but the tension is still there. 

Then comes the catalyst. We finish the 'on' period, and get some time off. Cue plenty off drinking, partying, and general debauchery. In this time I meet a lovely girl, let's call her Rebecca. We getting on well, hanging out a lot, the usual. Then she messages me saying things are going too quickly, and she wants to stay friends, but that's it. Sad times, but shit happens, I'm not gonna lose sleep over it. My team know about all this (we're close to we tell eachother everything). A couple of days later she messages and says she was sorry, she just got nervous, and wants to meet again. So that night we meet with Rebecca and her friends, she's with her dad cuz it's just been her birthday, we have a few drinks, then go to a bar where Tony and some of my team are drinking. Tony launches into her, threatening to hurt her if she screws me around again, verbally abusing her, saying that's she's slut and a whore (to her Dad), a genuinely unbelievable encounter. I'm shocked, completely and utterly. I confront him, he tells me that I should have expected it, I should have known what he's like, completely not accepting what he did was totally wrong. He keep this stance up. Things between me and Rebecca  kinda break down, again I'm sad but not gonna lose sleep over it. However I'm still bloody mad at Tony. He was  well out of line, and his refusal to admit and apologise rubbed me the wrong way. He has abused a member of the public, who he doesn't know, and her father, put our name into disrepute (Rebecca and her father were well aware of where we were working), and to make matters worse, the incident is being brushed under the rug by our team leader, because he's friends with Tony. Again, we move on, we don't want to ruin the team dynamic, it's not worth it over a girl. Fuck...

About two weeks later, I leave that job, partially because of Tony, and partially for other reasons. I leave on good terms, and the team leader gives me a very good reference, all happy as. However a week later I get a message from Rebecca saying she'd met Tony on a night out, and he'd been incredibly abusive to her, slandering her and telling vicious untrue personal rumours about her. I am fuming, however I tell her there isn't much I can do unfortunately, since I don't work with him anymore, and I know how things have been dealt with in the past. 

While looking for a new job, I meet a lot of old friends, who are mutual friends with Tony and my old team. When they ask why I left the job, I tell them, partially for other reasons, and partially because Tony was was an abusive alcoholic who needed to be babysat on a night out because he lacked self restraint and could not be trusted not to be horrifically rude to people he didn't know, and then to make things worse would not show any empathy or understanding for where he has gone wrong, and I did not want to work with him anymore because he made my life very difficult. I was generally pretty scathing of him, to people we both knew very well, as well as other people in the industry. 

Well this backfired on me. I got a new job, things are going well, and then my new team and my old team with Tony end up working next to each other. It's a little awkward but we're all grown ups. Or so I thought. A couple of days later I get the following text from Tony

Hi u/unofficial_ed ,

It has got back to me though quite a few people this side and in XXXXX that you have been talking shit about me. I know this for a fact and you slagging me off its not something I want to hear anymore ! I'm sure you don't want me to take this further!! So it's your choice if I hear you saying anything bad towards me again you will be sorry.

Kind regards 
Tony. 

Fuck. This message pissed me off, partly at myself because I really should be above that kind of behaviour, I was raised better than talking about people behind their backs, and partly because of the hypocrisy of it all. So anyway not wanting to start anything that I know I will lose (he is stubborn and judging from his message and past behaviour this could potentially turn violent), I apologise in text and in person. He seems cool with it, although there is still tension. 

So that begs the question; I slagged off someone I used to work with to our mutual friends, and others in the industry. Am I the asshole? 

TL;DR: someone I used to work with was a dick to me and incredibly abusive to a girl I was with, and in return I told our mutual friends plus other people in the industry about how he was a dick to me and incredibly abusive to a girl I was with. 