If a guy likes you, he will almost always be obvious about it; whether or not he is smooth or awkward about it, he isn’t going to hide it, and it should be very easy to tell.
At work, or at school, or within your group of friends, he seems to constantly be around you.
Sometimes friends who really like one another can pick up habits, mannerisms, and ways of laughing from one another.
Women, of course, are guilty of this one too.
If he is constantly trying to make eye contact with you, even when he is on the other side of the room, then something is probably up.