I think the most amusing (I honestly can't remember the first....) was a car with 3-4 college age ladies that yelled out 'Nice legs' or something to that effect as they passed by. (This was back when I was also in college, although probably 8-10 years their senior, and usually rode shirtless.) Unluckily for them, they caught traffic at the next light, and I returned the favor with 'Nice car' as I went by.

I'm pretty sure they all turned a brighter red than the car....