I think it's hard to tell straightaway. (Pardon the pun) But I've been in contact with many seemingly straight guys who I feel could possibly mess around with another guy. For instance, one of my former barbers is a very sexy guy, works out all the time, has a hot body, and i think he would "flirt" just to continue business with me and get tips. He was always showing me pics of women that he had "been with" and talking about his sexual encounters. Now he would flirt with me buy sensuosly and gently rubbing my face while cutting my hair, comment on my cologne and how good it smelled, and even play wrestle with me in the shop. He cut my hair for about 5 years, so I have countless accounts. I won't bore you with all of them, but hopefully you get the idea. Then there are two men at my job that constantly do too much. I don't know if it's a male bonding thing, or what, but one is like in his mid 40s, nice muscular body, and has plenty of kids and grand kids and has a girlfriend. He's always rubbing my stomach, hips, and back in an attempt to make me try to "play fight" with him and tell him to stop. If I was straight, I would not do these types of things with some man that I thougt was/could be gay. So in short, I think it's very hard to tell if a man will mess around with another man. But what's probably more important is figuring out if a/that man will mess around with YOU. I think men are very relational. For instance, I never witnessed my former barber flirting with his obliviously gay clients or other clients for that matter, and the guy at my job dosen't flirt with another guy at my job that is clearly gay. I think men, straight or gay, kind of KNOW when another man is attractive and that might spark curiousity in them. But it's been my experience that it takes time, and some time of inebriation, to coax them to a place to let their guard down. (Hope this added some insight)