Head Nod Hello

I'm sure many people can identify with this form of hello. It's usually done by guys to other guys. This is the problem I have. Is when I'm walking and there is a guy in front of me who looks like he is looking right at me, he then gets a little smile on his face and gives the little head nod. Naturally I feel flattered and also start thinking do I know him? I review the last few classes I have and the guys in my ward and just as I'm realizing no I don't know him. I hear him say "sup mike" and I realize that he is looking and smiling at the guy directly behind me. Then I feel lame because I've got this stupid bewildered smile on my face and have been staring into their eyes trying to figure out if I know them. I just hope guys are as oblivious as they sometimes are and don't realize that my stupid smile was geared towards them.