how do you tell if a guy is bi ?
Most Helpful Opinion
I'm not sure if there are any outward signs that can tell if a guy is bi, unless you see him dating both sexes.
Depending on your relationship with the guy your wondering about (if there is in fact a guy you're wondering about), you could always ask him, if he's mature he'll answer you as such and more than likely follow up with "why do you ask?"
Of course if you're not exactly close to this guy (intimatly or otherwise) then it's probably not a very good idea to just come out and ask him, so you're gonna be left wondering.