A sudden change of mind
I went in with every intention of paying for the drink of the person behind me at a coffee shop. (This was before Project Super Nice, or I would have followed through with that.) As I was standing in line, I started to think about all of the stories my sister had told me about her experiences as a former barista. Pretentious college students, arrogant professionals who treat the staff like their own personal servants at best, people who cut in line and demand to be served first because they feel they are just that important, people who throw their money at the barista carelessly rather than taking two seconds to hand it to them... the list goes on and on. Of course, every customer service job involves these kinds of incidents. It's just that I found myself thinking more about the baristas than the customers just then.
Event: I took the money I had planned on using and put it in the tip jar instead.
Reactions: I snuck it in, so I don't know.
Would I do it again? Yes.
Cost: Ten dollars.
Time: Maybe ten seconds.