You’re out to dinner with your friend. They insist on paying and you want to leave some kind of contribution but they just wont have it. A fun way to get them back is to do the pocket slip.
The pocket slip: The reverse of pick pocketing
Go to your ATM, pull out a crisp 20 and hang out with your friend until you know they will be removing their pants (this can get awkward and involve some uninvited sitting on their couch nursing a luke warm beer until the wee hours. We suggest hanging out with them near a hot tub). Once the pants are unattended, get sneaky and slip that cash in there. No note, no explanation. Just the joy you’ll have knowing that the next day when they are going to get their morning coffee, they wont have to charge it.