Experience: A free coffee, a stranger, and a decoration competition

The experience I designed is relatively simple, and it involves my favorite coffee joint, Everyman Espresso.  Here I am, outside:

My invitation consisted of a coffee cup, a free drink coupon (in the form of a buy 10, get 1 free card, completely filled out), and a note with instructions.

The note read like something like this:

1. Have a coffee on me (don't forget to tip!)
2. Collaborate with a stranger to decorate the coffee cup
3. Present the decorated cup to the barista(s) for judging, and encourage them to start an annual cup-decorating competition.

The idea was to see if I could affect change indirectly; that is, by getting someone to carry out my idea without me actually interacting with the people at the other end.  And of course, to get the person who received my invitation to leave ITP for awhile, have a delicious coffee, and interact with someone completely unknown to them.