carcinogenic fumes, litter, and fire hazards

As I was leaving the campus yesterday, I saw a girl finish smoking her cigarette and drop the smoldering butt in front of the music building (smoking is expressly verboten on campus). In a flash of inspiration, I grabbed it and ran up behind her at the stoplight as she was talking on her cell phone. As I handed it back to her, I said with a smile, in a low-key friendly sort of way, "Hi, can you do me a favor? Take this with you, don't leave it on campus? Thanks." I didn't know what to expect, but she took it from me, I guess to avoid having to interact with me; she dropped it again as soon as my back was turned. Another guy was standing at the stoplight with us and thought it was pretty funny. I'm not sure what I got out of it, but I guess that when someone behaves in a way that is an appalling combination of stupid and inconsiderate, it's nice to be able to point it out to them without having to use those precise words. I guess it has a nonzero chance of altering their future behavior.