Friend Sip
A "friend sip" is the absolute limit of liquid a friend is allowed to consume from your drink when you are polite enough to share (one mouthful). No more than a "Friend Sip" can be taken by a friend, preferably less.
*Starts Sculling your Drink* "Wow, cool your fucking jets, Starsky! That was a girlfriend sip! Give me back what you took.