To ask for your ideas to take petty revenges on an uninvited guest?

Buy some prawns on their use-by date and sew them into the hems of the unwanted person's bedroom curtains.

OP, why has your DM suddenly started visiting so often? And I absolutely agree with other posters: under no circumstances buy her house - find somewhere else that will be absolutely yours and nothing to do with her. If you start looking now, you should be able to move shortly after your finishes her exams. Does your DM think you like having her there, or does she know you resent her? I might have been tempted to say something to the effect that once I got out of her house, I’d make sure I never saw her again. Would she care? I just don’t understand a parent behaving like this towards a daughter - she must know that this arrangement can’t go on for ever, and that she’s hardly endearing herself to you.

Are you my ex-flatmate? If so, please turn the History Channel off; none of the rest of us are interested in how many people died in that plane crash, or why.

just got back on the laptop read the ops up dates, makes sense now, good luck

Did you know you can read the OP's updates?

@guestsareinvited- do not buy this house from her. She will still see it as hers.

Also in this visit, you need to have a chat about the rent. The rent you agreed to pay was for exclusive use, not only part share with her. Given she visits for so long but doesn’t pay towards the other bills, you’ve decided you won’t pay rent/only pay 50% rent for the time she visits.

I would get on with finding another house now. It could take until June to complete - most conveyances seem to take 3-4 months. Even with cash buyers.

You need to stop planning to buy that, make it extremely clear that you’re only looking elsewhere and LOOK. Even if you did buy it she would always feel entitled, kill that plan stone dead op.

You shouldn't even consider buying the house even if she stops dicking around with the price. She will continue to behave like it is hers even if you change the locks. Sounds like more hassle than it is worth.

Get your cat/dog/hamster to wee in their shoes.

Let them use your fresh milk but then swop the lid to one with a really old BBD and say "you didnt use that did you? That was my DC's science experiment for school. Oh dear. Well I guess it will be ok...?".

Spill milk in their car.

Rub a bit of garlic on a washable peice of their clothing. Not much, just enough so the smell annoys them but they dont know where it's from.

Consistently get their tea/coffee order wrong but if they raise it be dismissive. "I'm sure you said 2 sugars, oh well. I'll remember it for next time".

Be loud when they are in bed.

"Tidy up" their things. In fact follow them round tidying eg as soon as they've put a cup down "have you finished that? Let me take it out". People who do that make their guests really uncomfortable.

Put the TV on a tiny but too low for them to hear. That annoying volume where you can sort of hear it.

(Sometimes I find it cathartic to think of petty things to do to people who've annoyed me so I have many ideas. I will never do any of them but revenge can be fun to imagine)

Start using her room for storage. Little by little until there’s no place left for her to move around and to sleep. It’ll become unappealing to come and stay.

grow a pair dont let them in, lol, we must know who it is ie mum friend etc.

I'd start actively looking for places, making it clear that her house is off the table once you find somewhere. Go to viewings, search for them over the breakfast table. Don't give her the power to dangle the house over your head. Take it back.

Get one of these

It makes a mosquito buzz noise when its dark but as soon as a light is turned on it goes off.

https://www.google.com/imgres?imgurl=https%3A%2F%2Fwww.rexlondon.com%2Fsites%2Fdefault%2Ffiles%2Fstyles%2Fsquare_800px%2Fpublic%2F2023-11%2F30326-mosquito-sound-machine_lifestyle.jpg%3F_buster%3DWWu72oGV%26itok%3D1j4htjpf&tbnid=D0z3F7s73nScFM&vet=1&imgrefurl=https%3A%2F%2Fwww.rexlondon.com%2Fmosquito-button-classic-jokes%3Fsrsltid%3DAfmBOopHIVO9XdwvUhbCvaNPf2ing0HoOQmKfy8Lu6vXZOvMxB6Vd1ER&docid=K257EZ5T6X0mUM&w=800&h=800&source=sh%2Fx%2Fim%2Fm4%2F0&kgs=a11fc49eb45d66e5#piu=ps:6&sv=CAMSaxoyKhBlLUQwejNGN3M3M25TY0ZNMg5EMHozRjdzNzNuU2NGTToOSzI1N0VaNVQ2WDBtVU0gBCoxChtfVlV5cmFjWEpOTEtxeGM4UGxLQ0lnUUlfNDASEGUtRDB6M0Y3czczblNjRk0YADABGAcgyciOqwMwAUoIEAIYASACKAE

Whilst she’s there hold-off paying her rent, or pay her much less, take it as her contribution towards the bills. Unless she doesn’t use your water, gas, electricity, food, detergent or toiletries ofcourse.

Plus cook up a hot hot dinner, ‘Thai jungle curry’. And watch her sweat-out uncontrollably. 🥵

You're not uprooting her if you move somewhere else locally. It's still only March, she's not mid exam. Surely it's worse for her in this horrible passive aggressive situation, where you and your mother are at loggerheads?.
That's not a nice environment for a teenager.

Why don't you rent somewhere else?

Electric shower? Flick the fuse off, power to the shower goes off but cold mains water still comes through.

Ah, come on. She's still her mother.

Clear out the attic, garage, shed (or whatever) and pile the guest bedroom with absolute dross, covering every inch of the floor space. You're very sorry but the roof/garage roof is leaking badly.

Take the loo roll with you and back every time you use the bathroom.
batteries out of the remote and go out
change the wifi password
leave a pile of the worst bedding and towels on the unmade bed for them

Good god don't swap decaf for full caffeine! I have a heart condition, you'd kill me!
As for subbing in decaf, yeah do it, nothing as joyless as shit tasting coffee that doesn't even perk you up.

This. 👆don’t join in with this rubbish. Ultimately you have the final say in who is welcome in your house but if that’s not the case then remove yourself and don’t give them the satisfaction