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.
Idk trying to identify someone as bisexual is pretty impossible in my opinion. It's not like with "some" gay people where you can automatically tell "he's gay." Even if the guy is a bit femenine that doesn't mean he's gay or bi so it's better to not make assumptions and just ask them upfront.
Haha , man you people keep coming with these questions , if he's a freind of you'rs just ask him while you'r joking with him if not I don't think its a good idea to ask , by the way Why you care if he's a bi or not do you have a crush on him or trying to date him , just wondering .LOL
I'm pretty sure there is no real, 100% fool proof way of finding out if a guy is bi or not without just coming right out and asking him. I know a few guys who dress well, do their hair, stand up straight, have excellent posture, and people have told me "Oh, he's bi, you can just tell by the way he acts and dresses." And honestly, these are guys who grew up with only their mum and sisters, therefore giving him a more metro-sexual look. Guys are just as entitled to take more concern in their appearance as girls are.
So, in short, there's really no easy way of looking at a guy and deciding that he's gay, bi or straight. There are no visual signs for that. The only way to really get a definitive answer is to ask him out right and hope he doesn't take offense. Because honestly, how would you feel if someone walked up to you and said "Are you bi?" Pretty uncomfortable if you're straight, right?