While commuting, I've had two encounters. The first one was a group of twenty-somethings who told me they thought my bike was cool. I had just gotten it and loved the compliment.
The other was when I got caught in a really bad downpour. Fortunately, there was no lightening, but it was coming down like buckets. So I'm stopped at a traffic light, and this guy pulls up before making his right on red, rolls down his window and says, "It looks like you picked the wrong day to bike to work." I smiled and replied, "It's a beautiful day to bike to work!" We both enjoyed a laugh, and he drove away.