My first impulse was brutal, as they often are. (My mind '... moves in strange directions,' to quote David Lynch's 'Dune.')

Rather than the shock-and-awe approach, you could always just take a Polaroid while you're kissing and subtitle it something snarky which I leave to you, rather than suggest the rudest possible outcome.

(... and yeah, 'kissing' is not the rudest possible outcome. See? It takes forethought and effort not to go immediately for the jugular.)