When one person intends to make out with the person next to them, they proceed to rub their face (most specifically nose and mouth) against the other person's cheek, to send the signal that they are interested. If the other person is into it, they will turn their head so that they are face to face (or mouth to mouth).
Sarah: Hey, did you end up making out with Rob last night?
Jen: No, he was totally face gaming me all night, but I so was not having that.
Sarah: Ooh, rejected.