The Kissing Game
A and B play the intention of kissing each other passionately on the mouth. If you know that you’re not actually going to kiss, then you can commit yourself to that intention completely.
The game is to play the approach to the kiss, and at the last moment, to subtly change your mind; not to retreat, as you would if you wre playing a reversal, but to continue in the same direction as before, and instead of recoiling you let your lips just slide past your partner’s lips, as close as possible, without touching.
That is from the quite interesting Why is That So Funny?: A Practical Exploration of Physical Comedy, by John Wright. The book discusses how improv comedy "models" human behavior, and where else will you find a discussion of how the "Principles of Simple Clown" differ from the "Principles of Pathetic Clown"?