READ MORE: • Couple's Dunedin home smaller than a car park
"If all the mess isn't removed over the weekend all the evidence will be passed on to Edinburgh Council."
Thomson was understandably annoyed at her neighbour's tone - and the fact that they didn't sign off with their name.
She hit back with her own letter.
She wrote: "Dear angry sir/madame,
"Thank you for making me aware of the rubbish in my garden. I had no idea, but your passive aggressive threatening note made me notice – HORAY!
"I'm so glad you wrote to be honest, because now I know that someone else is concerned about the welfare of the garden (which no one else has helped with in the six years I've lived here).
"Next time it may be useful to knock on my door. Pop around any time.
"Also, if you contact the council, please let them know I'm still waiting for a recycling bin."
Her response was soon ripped down and replaced with more threats about phoning the council, but Thomson refused to back down, writing another note which she framed.
She again repeated her request for a recycling bin, explaining she had been keeping empty jars because she felt guilty - but unfortunately that left her cupboards smelling like garlic, which her cat does not appreciate.
Thomson shared the hilarious exchange on Twitter, dubbed "notegate", with the caption: "Walked into a passive aggressive note about bathroom rubbish from my FRESHLY done up bathroom in my garden (totally out of my control) threatening the COONCIL on me.
"They didn't catch me on my friendliest of days. How to be a cheeky c*** 101."
She even told the unnamed writer she was going viral on Twitter, telling them their conversation already had 2,874 likes.
Now the tweet has racked up nearly 2000 retweets and more than 13,000 likes.
Even her neighbours are getting in on her antics, leaving their own notes and stopping her in the street to talk about how funny it was that she called them a 's***ebag'.
One wrote: "Please don't speak for all of us! 'The whole stair' is NOT against Flat 1."
Upstairs neighbour Stephen Bridgman, 43, told MailOnline: "None of the rest of us are complaining, as far as I'm aware it's only one.
"Plus I don't even think it's anybody from this close that's complaining because the notes are on the outside door, they've not been put through her letterbox.
"I put the note up saying 'everybody in the close is not against her' because they don't speak for us all and that annoyed me. Nobody's speaking for me.
"But as far as I know it's getting shifted as soon as the landlord's back from holiday, it's no problem. It's a private garden anyway, it's hers.
"It's just unfortunate because her hands are tied, it's up to the landlord to get it moved."
Ms Thomson shared another update, saying: "I am back from gigging in Aberdeen and came home to this note. The whole stair is now involved. Other neighbours have now started leaving notes. It's Noteception. It's EastEnders for Piershill. #NoteGate."
She added: "Update: #NoteGate. Neighbours keep stopping to talk to me about my notes. They all find it amusing. No one knows the culprit yet but we have a sneaking suspicion of who."
Twitter users have praised Ms Thomson for her polite response, with one saying: "Beautifully written response Keli, fair play for not sinking to their level."
Another said: "Having read the thread, you're the hero we need in this world. Do you have a stylish cape?"
One individual wrote: "Haha class response Keli [laughing emoji]. Take it they never popped round?"
