I have a few.

If you're driving behind someone, they will slow down until you try to pass them.

A simple hello can either keep people from bothering you, or invite hours of their life story. Flip a coin.

Wearing Headphones on the city bus means nothing to anyone who wants to talk.

Feeding the city crows peanuts at your home will keep the city pigeons away.

Yes, it was [insert weather condition] a moment ago.