During my company's Christmas party one colleague got extremely drunk. He then went to me, put his arm around me and his hand on my behind. I found this both annoying and highly inappropriate and pushed his hand away. He did it again later in the evening. When he did it the third time I raised my voice a bit while telling him to stop and that was enough to stop him. However from his body language I think he felt like I overreacted.
I don't know this colleague very well. I have talked to him professionally and exchanged a polite sentence or two over the coffee machine.
Since I fear that he genuinely does not understand that his behavior was inappropriate, I would like to talk to him. My goal is to make him understand that touching someone's behind without their consent is not okay. Ideally I would like to make sure he won't do it again, but I mostly don't want him to be able to say (even to himself) that he didn't know he should not do something like that.
On the other hand I would like to make as little fuss as possible. His behavior did not scar me for life, I just found it quite annoying.
Another thing that makes me think he does not understand what he did wrong is that another colleague told me that this behavior was not unusual for that guy when he gets drunk. Said colleague however also said that the groping colleague is usually a friendly guy (when he is sober). He has also always been friendly in our brief encounters at the workplace.
I am considering talking to him one on one and just telling him that he made me feel uncomfortable. I am however afraid that he might just brush it of as me being oversensitive.
I am thankful for any pointers to how I can communicate effectively in this situation.