Some others have already had their say but I felt like adding my two cents as I feel this is extremely unacceptable. I'm pretty sure if any cis-guy tried to throttled another cis-guy he'd be punched in the face or it would get nasty very fast.
Keep this in mind, some people (and I mean only a handful) who show this kind of behavior could either be sadistic in nature or be unaware they are sadistic (and I don't mean cut you open and laugh as you bleed, there's mild levels of sadism as well) and if he happens to be either, though more-so the latter, he may one day have his hands around you and not stop because he gets too caught up in it. Then you are in serious danger and if guy B isn't around to yell at him, and you've never established boundaries, trying to stop him might turn very very ugly.
It's kind of different but I work on occasion with metally disabled invidiuals and I remember this one man, he would touch my arm (I didn't pass back then at all) and 'flirt' at me. When one of my co-workers noticed they came up to me and told me never to let him touch me. Just the seriousness in her voice made me aware that it was much more than just touching my shoulder or hand and since then i've always been a bit leery about people who I don't know touching me.
Me and my boyfriend, even before he was my boyfriend, would roughhouse and I really enjoy it. I like to test my strength against him, he's bigger than me and made of muscle so I find it very satisfying when I 'win'. But I know that if he ever told me to stop, or if I ever told him to stop, that it would stop. I NEVER feel endangered. I also have a rule, and it's a rule across many practices (BDSM for example) that no one is to ever cause physical harm to your face. You can extend that to your neck too. No one should EVER go anywhere near your face in a threatening manner. If someone punches you in the face you have every right to curb-stop them in my humble opinion.
I also know from an experience that I don't want to get into, how fast someone can go into the red zone. It has been described to me as "you don't know sense, you don't know what your doing is wrong, you're just focused on the goal. You forget your own strength and you can do terrible things before you feel satisfied enough to come out of it."
So please, please for your safety, next time he goes for you, make sure you are somewhere where there are people who, if they saw someone being assaulted, they would either call 911 or intervene, and tell him NO. Established that you do not like being throttled and he is not to touch you aggressively (or ever, if you want) again. If and when he backs down and says ok, go on like it never happened. You have to let things go, excuse the silliness of this sentence, but you've disciplined him, and now you need to revert back to normal and if he does it again, warn him again. If he does it a third time, stop hanging out with him until he's ready to treat you with respect.