When the sheila wants to move in

• Saying something like "Do you want to move in?"
• ... or "This place gets a bit lonely at night" (Get Hard, ya big blouse!)
• Letting her leave her stuff at your place without you burning it on the front lawn and saying "oh sorry, I thought you were done with it" when she complains (This includes books, clothes, pets, her Datsun bluebird, etc)
• Letting her stay for increasingly longer periods of time. (It starts with a long weekend, then they wear you down by staying over when they're on holiday, then saying things like "It's only two days till the weekend and I can't be bothered going home so I'll just stay here tonight", etc)
• Not shouting "NO!" when she mentions moving in.
• Nodding - accidentally or intentionally - when the topic comes up when you're out at dinner with mates..

Because if you let her move in, you are - as the saying goes - screwed.

Moving in - Stage One

Stage one of a move is the best it's ever going to get - it's downhill from here. If you think it's a bad plan at this stage you need to hit the abort button - which usually means inviting shitloads of mates to come and stay at your place for extended periods and drink booze and watch tv all day every day and not wash. One of them getting a stripper in is usually golden.
As stated, this is the best you're going to be. She's happy to be moving in and will do those nice things that she thinks you'll like, like picking up your clothes, cooking your favourite dinner (barbecue), doing the dishes and generally keeping out of the way...

Moving in - Stage Two

Stage Two is where you notice the slight changes about the place that might mean nothing, but then again might mean something. There's some loo freshener in the toilet and one of those smelly things in the bowl. Your boots are tidy outside the back door and the dishes are only washed, but not dried. Your clothes are pushed into a corner.

Moving in - Stage Three

Stage three is where you finally realise that you're screwed. Dishes regime comes into force where 'If I cook, you should do the dishes' is the rule. Also, you'll notice that your possessions have started disappearing. You'll find them tidily in a cardboard box somewhere out of harms way, as the sheila starts 'upgrading your life'. Note that they're not thrown away, they're just tidied - out of the way. Maybe a picture of her folks or some flowers will appear on the wall where the Lion Red poster used to be.

Moving in - Stage Four - Welcome to Hell

Stage four is where the sheila has given up any pretence that everything you own is crap and that everything she owns is the greatest. Your pots and pans have gone to a charity shop - but only because they won't burn. Your bed cover with the impressive picture of a lion on it has gone - noone knows where, but you did notice a rank burning smell one day when you were working out in the shed. Come to think of it, all your 'comfortable' clothes went missing around the same time.
And don't even think about not doing the dishes.

And cooking dinner - and not that crap that you eat either, a healthy meal - with salad.

Moving in - Stage Five - Getting the Mrs to move out

Don't bother, it's not going to happen. She's in there to stay and may as well be a reinforced concrete garage for all the likelihood that you'll be able to move her.

The best plan is to just go down to the shops for a loaf of bread and keep bloody driving...