Touching
Depends on his and your intentions. If the shared intent is sexual, go with it. If there isn't a sexual intent, return the gesture, then step back. Touching my cock is not a standard part of conversations for me. Neither is touching someone else's. If such things happen during a conversation comparing dicks, I think it's ok then too, but otherwise I wouldn't appreciate the groping.
It happened to me once at the nude beach. I was there with my boyfriend, who went for a walk. Some guy came up and started chatting with me as I was sitting in my chair. I was fine with it until he grabbed my dick. I brushed his hand away and he apologized. Our conversation wasnt remotely sexual in nature and I wasnt doing anything to lead him on. I thought it was kind of ballsy to just grab another guys dick. Now, if the context lends itself for such an action, then ok, but to do it out of nowhere, and on a public beach, yes thats creepy.
I actually had a situation in a hot tub one time. There was a group of us having a decent conversation. The guy sitting next to me was a bit under the influence of alcohol. He was was wondering where his husband was. Not withstanding the rest of the group was conversing well. It was one of those hot tubs that the temperature was a bit too high so I sat up on the rail. The next thing I knew I had a head in my lap and a mouth on my member. It took a few seconds to get my senses. The same guy who was looking for his husband was now preoccupied with another task. It was a bit creepy. I gently reached down and lifted his head out of my lap. Fortunately one of the guys in the tub recognized my shock of it. He became my partner for that moment. I don't think anyone wanted a jealous husband rushing the scene. One good thing about it the guy who stepped up to my aide has become a good friend. We have been making an annual camping event since then. So yes it is a bit creepy and awkward to be touched uninvited.