‘Shacking up’ means moving in with someone of the opposite sex with the intention of coupling without license or permission from family, friends or society. The word ‘shack’ hints at ‘badly made, a dwelling hastily flung together’. To say Marvin and Linda are ‘living together’, or that they’ve ‘moved in together’ is one thing: but to say they’ve ‘shacked up’ is to put them in a specific place. A picture comes to mind: of dull-eyed Linda wearing a tube top. Her legs are skinny, her hair bedraggled. She leans in the doorway of a cabin, her attitude suggesting she’s holding the thing up. Marvin, who is still in bed, is unshaven. He has a course laugh and nicotine-stained fingers.
The fact is, you can’t ‘shack up’ in the Hilton. You may take tea and request the services of a gigolo, or find the afternoon sun exhausting and go to your room to lie down, which is where your friend will find you when he comes back from buying theatre tickets. His name is Roger, she is Roxanne and they don’t plan to marry any time soon because they’re already married to people who they like well enough but who in some way have been a disappointment. Roger and Roxanne are having an affair. Can you hear the lightness in the word? An affair is a fleeting thing that lasts as long as the weather holds. Society does not condemn this pair; it merely lifts a bare shoulder and shrugs.
‘Having it off’ speaks of an absence of care or love; an act of no greater consequence than brushing one’s teeth or doing the washing-up. Hugh can be ‘having it off’ with Penny or George, though not often at the same time. But here the door closes on the scene because the public doesn’t particularly want to know what goes on. The expression may be accompanied by a raised eyebrow or a knowing leer, but that’s as far as it usually goes.
Hugh and George and Penny live in a village on the outskirts of London or Manchester and commute to the city by train. They wear mackintoshes when the weather is dull and shoes polished to a brilliant sheen when it’s not. It’s important that one wear well-polished shoes if one is ‘having it off’ with someone, especially if all two, or three, work in the same office. But such a shine would be totally out of place if the trio were ‘shacking up’. Just think of the noise they would make.