Thanks, everyone, for the feedback. I did have an unofficial talk with the office manager. I didn't say who it was who did it, or file anything official, so hopefully there won't be any negative repercussions for anyone. She was really nice about it, although she didn't tell me anything besides what I already know. It was kind of reassuring to have someone respond thoughtfully--my supervisor sort of blew me off after it happened, and I'm not sure if anyone else knew what happened and why.
I was already planning on quitting this job before too much longer, and now I have even more reason to be happy about that prospect.
@Fnord, you're coming across as really hostile towards me right now, and it's bothering me. Are you seriously implying that this guy is about to, what, rape or beat someone? I've looked into the legal definitions of assault when other people have touched me like this; as much as it upsets me, I've never found anything that says it's a crime, if there's no malice, threat, injury, etc. Please tell me if you know otherwise. That would be a lot more helpful than what you're doing--pretending I'm a victim and then victim-blaming me.