the drive-by pickup?

Yesterday, I left my usual Sunday afternoon dance class especially sweaty and disheveled. As I was on my way home, I stopped at a red light. I turned my head and saw a guy driving a black car 2 lanes over smiling and nodding at me. I turned away. I turn my head again and he is still smiling and nodding. Now I'm wondering what's going through this guy's head. I can't possibly look remotely attractive since I'm all sweaty and nasty. Does he think I'm desperate or something, like I'm just waiting for my dream man to pull up in his beat up old Corolla and whisk me away? Does he think he's going to get me to toss him my number through his open window? Does he think I'm going to just get up out of my car and jump into his? Does he realize he's only making me more uncomfortable by the second?

The light changes to green and I drive off as quickly as I can. But I am still left to ponder, why do guys do this? Is there a portion of the male brain that actually thinks making eyes at chicks at stoplights is going to get them laid? Can someone please enlighten me on the psychology behind the "drive-by" because this whole phenomenon is just plain baffling to me.