When you have knives held between the index and middle fingers on both hands with the blades held just so the flat part of the hands on the palm lines up with the blades held in between the index and middle fingers and with the blades held flat against the palm and with the point of contact for extrajudicial instrumentation extending up from in-between the two fingers to make almost a fist bump type carry for a duel held combat grip. Don't slip and cut yourself.
I'm going to get Red hands when I go to the bank, they won't know what took their money.
A northern irish tradition of, when your friend turns his back, SLAP HIM ON THE BACK OR ASS AT F U L L FORCE.
If you have a Northern irish friend watch ye back
When someone is striked on their (often bare) back with the palm of the hand, leaving a red imprint or red hand on their back. Can be done in the changing rooms or any other opportunity