What's the last good deed you did?

[Duchess]

My daughter talked me into waiting in line for 20 minutes at McDonald's and when I got up to the window to pay, the girl said the lady ahead of me paid for my meal. I thought she meant that our tickets got mixed up, but she said that the lady offered to pay mine. I have no idea why she did it other than there are two drive thru lanes that merge together and i let her go ahead of me.

It's a "thing". I read about it being done here all the time, usually at Starbucks. Pay it forward.