I don't think that's actually helpful advice.
Eventually it was beaten into my skull that you Americans have serious issues about weight. Over the past two decades I have come to understand that in this country, saying your girlfriend is fat is on par with shagging her sister at Thanksgiving.
Frankly, you're stupid.
But this guy with the "lose 20 and I'll marry you" is even stupider. (So was shacking up in the first place, but hey, nobody pays any attention to my "antiquated" views on that subject, either.) I spent a lot of my youth abroad, and I managed to figure out the American thing with fat already. How the Hell did someone who went to high school here miss that?!
But let's talk motive. Americans equate marriage with the wedding, being congenitally incapable of identifying the legal and economic ramifications of the institution (i.e. the reasons it exists). Thus, a perfect wedding equates with a perfect marriage. Women fantasise about it all the time. The wedding industry serving those fantasies is a giant, terrifying, all-consuming monster, coquettishly done up in a white chiffon dress. The astonishing array of bullshit all participants must endure in order to conform to these elaborately codified fantasies is far more voluminous than the colic capacity of every bull that ever lived anywhere. Here we have a man who, in the face of this terrifying ogre, has the courage (or sheer idiocy) to hold up the slenderest reed of masculine desire.
The correct response here isn't one of vindictive leave-taking. No. It's time to bargain. In other words: "I'll fulfill your fantasy of making everyone jealous of your bride if in exchange you do these other things about on par with losing a couple stone." Then you work together to make your sick theatrical production a reality. Dropping twenty means you have every right to demand everything from the coach and four down to a properly fitting cummerbund on every monkey in the house, and a professional organist with more fingers than a New Jersey turnpike.
And if Mr Vain isn't up to the challenge, then you decide (again, together): Are we gonna get married like the real human people we are, or am I going to go and find myself a man who isn't such a total chuckling numbskull?
Personally, my wife and I went for theatre, and I don't regret it. I figured I'd only get one shot at putting on that kind of show, and so far I was right. I cut my hair, worked out, and drove the florists and caterers like a dominatrix competing in the Iditarod. But I bleeding well knew the whole thing was a fantasy, and I'm packing the spare tire to prove it; a spare tire my wife tolerates because, dammit, when it's snowing out and she wants some freakin' chocolate, I'll go out in the snow and get her some. Fair's fair.