Most Helpful Guy
Depends on the guy, and depends on his friends.
I've never really taken a vacation with just the guys, unless I want to argue that business trips are "vacations," which - believe me - they're not.
If I had some time alone, I would probably go SCUBA diving, get certified as an underwater rescuer or photographer, splurge some serious money on some deep sea underwater photography equipment, and take really amazing pictures. That, or I'd just dive in less than 30 meter depths for a few hours a day, and get the nitrogen out of my system before I flew back home.
Now, if I'm with a group of just guys, I'm basically stuck with idiots the whole time. I suppose it's better than being stuck with someone that's always anxious you're going to die. But, I'd be in the uncomfortable position of pretending I'm totally cool with just drinking socially for 12 hours a day and joining in on the conversation to comment how hot every other girl that passes by is. These are male social bonding rituals that I don't have the patience for anymore, and hence, why I've never really been on a guys only vacation.
I agree with shadowscapes. It all comes down to trust. You have to trust your partner. If you don't trust your partner, you both suffer. For example, I watched Man of Steel with my girlfriend yesterday. She wants to go see it again today, but I'm busy today with other things. So, she called up my brother's friend (a guy, let's call him Henry), to go see Man of Steel again. Now, I know Henry likes her in a sexual way. I also know the only reason she's seeing Man of Steel again is because she thinks Henry Cavil is hot. I think Henry Cavil is hot. But I didn't even give it a second thought when she wanted to go see it with Henry.
Why? Because I trust her. We have a relationship of blind trust. It's its own incentive to not do anything funny, because both people are afraid to destroy, ruin, or lose that relationship of blind trust. Think of it like the marriage between game theory and the endowment effect.
Now, I suppose you could have a relationship of zero trust, or only "token" trust, where people had to "earn" trust or else they were presumed guilty or potentially guilty. In that relationship, nothing is really "lost" by doing anything funny. Plus, there are no real benefits of trust until 50 years down the road. So, people are actually more at risk to do something funny in that relationship dynamic, either because they want to see if they can get away with it, out of frustration of feeling controlled or oppressed, or because of resentment towards the dis-trustfulness of their partner.
All you have it trust in a relationship. Without trust, there's no relationship. Trust is the only thing holding two people together voluntarily (i.e., not by financial necessity). So, it's your choice whether you want to presume you have a relationship, or you want to presume you don't have a relationship.