The anonymous man posted on Reddit that he, his wife and their child had been planning on visiting Venice as it was his wife's "dream".
Venice has always been my wife's idea of a romantic city, so it's been her dream to go there," he said, adding that his mother-in-law was invited after she found out about it.
"My wife was very supportive of this idea, but I was more reluctant," the man said.
"My wife planned everything, booking the hotels and the restaurants."
Things took another turn when the wife book just one room for all four, meaning his mother-in-law was "constantly in my space" and using their hygiene products.
"It is very unhygienic to me and I don't like that she was sitting on the bed that me and my wife share, as I am a very private person," the man said.
"She also rummaged through our suitcase looking for a hair tie, and it really irked me that she did so without asking me. I don't like the thought of her looking through our stuff when we're gone, so I locked it."
But the man said the "final straw" happened when he found his mother-in-law had used their toothpaste, which made him feel "ill".
"I don't like the thought of her putting her toothbrush close to (or even on) the toothpaste nozzle, and I was ill the more I thought about it," he said.
"I asked MIL if the only reason she came was to freeload off of me and my wife, as she didn't pay for any of the expenses (hotel, amenities, food), only her own plane tickets. I said that I've asked her politely several times to stop using my wife's stuff, especially because I share it with her and it's very inappropriate."
The man said he then changed the date of his plane ticket to go home, despite his wife's anger.
"I feel bad that our daughter was caught in the situation, but it was really not acceptable what my MIL did and I had to set some boundaries before it gets worse," he said.
The post was shared to an AITA thread, and majority of Redditors decided the man was an "*ssh*le".
"Your wife books the wrong hotel room so your solution is to abandon her on her dream vacation, forcing her to care for your high-maintenance kindergartener on her own? Couldn't you have booked a separate room for your MIL instead of abandoning your wife and child?" one said.
"You are actively harming your marriage by continuing to ignore her calls. All of this happened because you couldn't communicate like an adult (how hard is it to say 'let's go buy another toothpaste so you don't have to use ours' for example?) and now you're doing the opposite of damage control by avoiding her on purpose and claiming that it's for your mental health," said another.
