Went shopping at Sainsbury today and asked for £20 cash-back when I paid with my card. The cashier made a misstake and picked up a £20 note twice, hence giving me £20 too much. I noticed it immediately but didn't say anything; I just put the money down, said thank you and walked off as calmly and quickly as I could.
Yes this is naughty, but Sainsbury is a very big company and it was their fault. That's not the point. The point is the intense happiness when a thing like this happens! It more or less cancelled out my last visits at Sainsbury.
I guess I could bake in an excuse about me being a student in this proclamation of guilt.