To humiliate one of your protagonists is wonderful, but to humilate both is divine.
Love drives us to extremes, and romantic comedy couples caught in the act of loving or denying love are already taking their emotional investments so seriously - or protesting them so fiercely - that they're ripe for major ridicule.
The beautiful thing about this technically terrible bit of business from The Proposal (its contrivances are wincingly clunky) is how it simultaneously turns both of its protagonists into equal objects of abject humiliation: it's a Scene We'd Like to See of primal simplicity. These two people have spent the entirety of the movie thus far attempting to deny a physical attraction while faking marital intimacy; they're two heads denying the bodies they're attached to, so when body meets body, both leads are reduced to the most amusingly inane protestations:
"Why are you naked?!"
"Why are you wet?!"
What else need be said? This is the essence of romantic comedy horror: we have met the enemy, and it is being human. It's great when one protagonist is shamed and humiliated, but if you have the opportunity to make both of your leads suffer, pile it on. From the black & white indignities of Cary and Katherine losing their cool in Bringing Up Baby to the technicolor widescreen food-poisoned exesses of Kristen & co. losing their collective lunch in Bridesmaids, humiliation has always been the coin of the realm in rom-com-land.
Loss of dignity is this turf's delight, so double up on the Passion and its Punishment and your audience's laughs will be twice as loud and long.