You can usually tell that a guy likes you when he ditches his boys to hang out with you. If he likes you enough, you get to meet the non-mutual friends...
when my guy friends likes a girl they will ditch me and my gf so they can go out with the girl and also make lame excuses... If I like the girl I would ask her to go hang out alot and it's usually me and her only...
Some tell-tale signs: he will go out of his way to see you. he will make excuses to talk to you. he will get jealous if you spend more time w/other members of the opposite sex. he will do sneaky things to try to get to know you better, like find out what your hobbies are, etc. depending on how old you guys are, he will not be afraid to look like an idiot in front of you.
how do you know if a guy likes you?? easy!! when he talks to you.. asks you out to hang out.. calls alot.. looks at you.. pays for you .. always talkin about you.. and getting to know you