On a weekend course a few years ago that was about getting in touch with yourself - and involved nudity and some touching of other people.
One exercise was to touch another guy's cock - did this with a few guys, one was an older guy who was one of only a couple who had admitted to having never touched a guy before.
He was cut - I wasn't at the time - so he asked about the foreskin, how it worked, so I told him, showed him and encouraged him to try - I started to thicken, and am sure I would have got rock hard if he had tried but it was a step too far. Unfortunately it was the last of the exercise so we had to move on, otherwise I'd have been happy to be the model.