There is a massive amount of fascination in most men for this sort of thing. When you think about it, a guys best toy is his dick. Most men absolutely love their dick, they love how it feels, there's an almost inbuilt fetish for cock in all men IMO. Everyone has a line they don't cross though, for some it's basic nudity, they can't even be in a room with another naked guy. For most others jacking off together isn't considered sexual, for the majority of those men that will, swapping hands is the absolute maximum.
There are a very few who are more inclined to be experimental and go further, but they are quite rare amongst men who usually maintain a strict label of heterosexuality.
Generally, men are more inclined to consider jerking with a guy if it's not about sexuality. It has to be discussed as a hobby, or a "bloke" thing. Under no circumstance is it advisable to discuss sexuality if this is what you want to do with him, that will just remind any straight guy of the connection between what you propose doing and "being gay".
The best situation/scenario, is to find a male friend who you think would be more open than most. You need a guy who isn't ashamed or embarrassed to show his dick. Don't choose a male friend who ALWAYS uses a cubicle when you're at a bar!
Next, arrange a convenient time or situation. Invite him over for a beer, play cards, or ask him to help you with some DIY (the manlier the better),
Alcohol always helps, but not too much. Incidentally, pheromones also help, and no I'm not kidding!
Previously I've used the above excuse (DIY) followed by a beer, and then mentioned some great porn site I'd found. We got it up on the TV and had a laugh about it for half an hour. Once we were on the second beer I suggested I'd need to have a wank, and asked him if he'd freak out about it. He said no, and so I got my boner out.
He was conveniently sat at the end of the sofa where my lube was hidden in a cabinet, so I asked him to pass it to me, which he did. Then he got his own dick out and went to work.
This guy was always straight in my opinion, but we'd known each other for a couple of years already, and I knew he was almost always horny. All it took was a little beer, some appropriate porn and me showing my dick first, from then on he was openly fascinated with comparing dicks and watching me stroke mine.
We met up to stroke a few times after that, and progressed to stroking each other once we'd watched some bisexual porn (by mistake
)
Unfortunately, we parted ways.
But I'm working on my next guy.
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Male Pornography/Sexuality Survey, please take part guys! (warning: blunt and frank language throughout)
Copy & paste.
http://www.esurveyspro.com/Survey.aspx?id=93aacfa8-e26e-47ed-818d-03fce8ecbc8e