The only time I had to deal with a situation like this, the dude was very, very drunk. I walked over and led him aside, telling him that he was making my gf uncomfortable, trying to be a diplomat. His response was to describe exactly what he was going to do to/with her. In XXX detail.
I reacted badly, kneeing him in the groin as hard as I could. He was so drunk he never saw it coming. He collapsed and we left. I was afraid I might have seriously injured him, but never heard anything.
This happened to me years ago when I was on a date. Angie was stunning, a cross between Connie Stephens and Barbara Eden. I stepped away from our table to piss, came back and this large Aussie fella was sitting in my seat. I reached over and slowly but firmly cinched up his loose tie and told him that unless he wanted to be buried in that suit he needs to remember that what’s mine is mine and he better fucking not forget. He left and Angie smiled, turned to me and whispered “I liked that thing with the tie.”
You tried to resolve the situation without escalating it. He mades it clear he knew the relevant facts, didn’t care and was going to be pushy. You struck the first blow before he did. I don’t see the problem.
Perhaps it’s because he was drunk and wouldn’t have acted like that when sober? If someone is a pushy asshole when drunk, they shouldn’t drink.
Is that a movie/show/book reference I’m not getting or do you really make death threats over trivial matters and consider women property?
The OP as framed is far too easy. It’s not even covered in Cockblocking 101
You come back from the restroom say hi to the guy and ask her if it’s her shot or yours.
That takes out 95% of everyone. If the guy is still there, you say conversation at him as take your shot and she moves to take hers. Cockblock.
When do we get to the difficult questions?
Seriously, this isn’t a hard situation. She’s your girlfriend. You have nothing to prove and you don’t want a girlfriend who wants her boyfriend to go all ape shit.
One time my girlfriend at the time and I were playing foosball and two guys challenged us. My girlfriend wasn’t that good and one of the guys was better than me but the other one sucked. After the first game, the good guy challenged me to a game and the poorer player used the time to try to move in on my girlfriend.
Fortunately, I was already out of junior high, so nothing to prove. This was a tiny bit harder than the pool example, because I was busy and the other guy wasn’t. In fact, I had my hands full so I wasn’t paying that much attention until the end.
We finished the game and walked back to the bar.
What is the other guy supposed to do?
I would walk up, ask her if it was my shot and stand close enough to her to let the guy know I was more than just another guy to her. I would want to stay close enough to hear her rip the guy a new one verbally, 'cause it would be funny. Only if he didn’t get the message would I feel like I had to step in and it wouldn’t need to be anything physical. I would just step close enough to him to distract him from my gf. Actually, that is basically the same way I would deal with someone messing with any friend or family member - stand close enough to let the drunk know he was dealing with a team.
Usually the guy is too drunk to be thinking properly but even drunks looking for a fight are easily distracted.
QFT. Fighting is always a last resort, and you should really never escalate a situation; even if it means leaving early or buying an asshole a drink.
I walk up to my GF as if I’m some random dude in a bar and ask her if she wants to make out. It works about half the time!
So, the other 50% of the time she makes out with the other guy?
I’d just start the night with “Hey, you look pretty hot, I think we need a plan of action. What am I gonna do if I come back from the bar to find you surrounded by drunken horndogs? Should I rush in with a broken bottle and a Chuck Norris roundhouse/leg sweep combo, or can you hold your ground until I get back?”
I hope you gave her the old heave ho. Sounds like she had some kinds of issues, and was working it out by putting you down just for trying to be helpful.
Definitely. Real women want guys to fight over them. The hard part is figuring out if they’re going home with the winner or the loser. So after you knock him out, kick him the balls a few times, that way if she goes home with him he won’t enjoy it.
25% of the time with the other guy, the remaining 25% with both guys 
We don’t hang out in saloons much, but I’ve seen a few guys attempt to chat my wife up when we’re at the gym or grocery store. I just watch with amusement for a few minutes while she shuts them down, then walk up and address her in Portuguese. They get the picture.
I’ve had it happen a few times. It’s almost always best to initially let your SO handle the problem (it happens to guys, too). 90% of the time, their lack of interest and/or retreating works (most “players” won’t pursuit it, as that’s time they could be spending on the next one).
In other cases, I’ve made my presence known by interjecting then removing ourselves from the situation, as if we have something better to do (such as lets go dance/get a drink/leave, etc.). No sense in being macho and standoffish, especially at bars/lounges/clubs where people have friends or you’re likely to get arrested.
The worst cases are almost always drunk people, though. I’ve seen some terrible things happen, here, especially if they are aggressive drunks.
Ask her if she’s given him a copy of the Watchtower yet.
As it happens I have seen this play out, with the man who is now my husband. Before we got together, he was quite the player, loved the ladies and the ladies loved him. He was seeing this tall (he was actually shorter than her, being the exact same height as moi!), beautiful blond, and they frequently drank at the bar I worked in. And they always stood right beside the service area and talked with the staff.
And every time he’d excuse himself to visit the washroom, men would flock over to this woman’s side and put the smooth moves on her. I heard it all, “What you doing with that short drink 'o water?”, “Come and let me buy you dinner!”, “Want to get out of here, I know a place…”, etc, etc. on endlessly.
And she never even made eye contact with any of them, just faced the bar and drank her drink, all the while saying, ‘No thanks, not interested!’, politely. On the occasions when he’d return and the guy would still be there, he did absolutely nothing, just let her turn entirely away from the interloper and engage in conversation with him instead. Message sent and received without the slightest confrontation. Sometimes it was men he knew, and he’d just shake hands and say ‘hey’, like they bumped into each other at the corner store!
I don’t know if I was more stuck by his confidence that she couldn’t be swayed, or his awareness that she didn’t need anyone to step in, that she’d take care of it just fine on her own.
Make eye contact with woman
Ask “Are you OK?” This is best done silently from behind the other guy if possible.
Respond accordingly.
There’s no need for violence or aggression at all. Just go back to your girlfriend and start talking to her like she’s your girlfriend, which she is. She will prbably move so you are between the two of them. Hell even introduce yourself to the guy while maybe putting your arm around your girlfriend. 90% of the time they’ll get the hint.
I have had this numerous times and really can’t recall doing anyhting special beyond making it obvious she was with me. A few years ago I took a girl to a kariokibar because she enjoyed singing. After a couple of numbers a so called gentleman joined her for a song, and then another having his arm around her shoulder as they sang. I didn’t give it too much thought until he picked up his drink and moved it to my table and scooted up next to her. I asked him if he was blind or just stupid and gave him a stare indicating I was ready to kick his ass. He promptly moved. Now I am getting older and was wondering how I would have handled that same situation if he would have been some big buff dude 20 years younger than me. I would proably handle it the same way but not sure what the outcome would be.