Aggressively sexual men are really putting me off volunteer work. What should I do?

I'm a 22-year-old gay male living in Texas. About two months ago I started volunteering at a local HIV/AIDS resource center and I've really enjoyed it. It's a fun atmosphere and the job is really easy. There's only one guy at the place that puts me off with inappropriate remarks, but I think he's taken the hint that I'm not interested and hasn't said much to me in about a month now.Volunteering here made me want to do some more volunteer work in the community. I've done 3 events so far and every time older gay men (that were also volunteering) have made very inappropriate advances on me.At event #1 a guy invited me over to his house to go skinny dipping with him and his husband. I had literally spoken about 5 words to this guy throughout the night before he came up and bluntly said he and his husband are voyeurs and they just wanted to watch me swim around and give me free alcohol. I was pretty speechless.Event #2 wasn't bad. A fellow volunteer asked me to go home with him twice but that was it. Nothing crude and he took the hint. I just didn't go to this event to find someone to hookup with.Event #3, which was Saturday, another volunteer had been making a lot of inappropriate comments throughout the day and it all culminated with him coming up behind me and embracing me. This one really pissed me off. I shoved him back and said "What the fuck are you doing?" Then everyone looked at me like I was the crazy one. He said something along the lines of "I was just messing with you." and someone else said "You really need to calm down." I left.I don't know what to do here. I like volunteering and I want to help the community, but not like this. For now I think I'm going to stop doing anything other than my weekly stuff at the resource center. I just want to figure out how I can volunteer without being forced upon like this. Has anyone else experienced something like this?Also, before anyone says "report it," two of these three events were one-day things sponsored privately and the people to report were friends of the person to report to. I'm really at a loss here.