So there's two threads on this, but they don't really explain the concept too well. The idea of "Pay it Forward" is a concept that started in a book called, "Pay it Forward" written in 2000 and a movie that came out on it a year later.

Basically, when someone does an act of kindness to you, you pay it forward by doing an act of kindness to someone else. Then they'll do it for someone else, and to one. It creates a butterfly affect where someone you will never meet will do something for someone else that you will never meet, all because you paid it forward. Therefor, your good deed could very easily change the world, which is the idea behind the original book.

To learn more, here's a link to the Pay it Forward Foundation.

http://www.payitforwardfoundation.org/

Start paying it forward now and get the cycle going. Your good deed could change the world!

someone did that at a starbucks near my city, everyone payed for the next person's drink until some jerk decided not to pay for the next person

0_0 it was super cool