Ms McGuire's dish from Melbourne's Kettle Black cafe included two slices of toast, half an avocado, a slab of feta cheese, a wedge of lime and a sprinkle of kelp salt.
Her post on Instagram, which has received hundreds of comments and likes, showed how the order was plated.
"I'm not sure you guys will ever fully understand the level of annoyance I felt being handed this alleged 'avocado toast with feta' breakfast that cost $18 today. 'Pretty deconstructed, isn't it?' I dryly remarked to the waitress, to which she smiled enthusiastically and nodded." she wote. "What f**king next. Being handed an avocado seed and told to farm the land and grow my own crop over several years before returning to the cafe to finally enjoy my breakfast?
"Eighteen dollars what a privilege there goes the dream of a mortgage lol the boomers were right."
"What a load of wank," one commented.
"Big profit margin on that there plate!," another added. "It's gotta be some sort of sick social experiment … I'd be fuming too."
Speaking to news.com.au, cafe manager Tim James said the avocado on toast was one of their most popular menu items.
"This is how we have served it from day dot, which is four years ago," he said. "It's half an avo in the skin, which pays homage to the avocado and the farms.
"Then you make it yourself, and design your breakfast your own way. We have some citrus on the site and you can add whatever you like."
Speaking of Ms McGuire's reaction to the dish, Mr James said every customer had a "different expectation".
"You can't please everyone," he said. "We can add things if they are not happy, but we have served it like this for four years and it is one of the most ordered dishes on our menu."
Ms McGuire said she didn't complain to the cafe owner, and will "write it off as experience".
Earlier this year, a cafe in Newcastle on the NSW mid-north coast was slammed for serving a $7 Vegemite toast.
Instead of serving the toast with the condiment on the side, the $7 dish was served on a wooden board. The chefs quenelle the butter and pop it beside the toast, with a dainty little microherb leaf resting on top.
Finally, they get a great big blob of Vegemite and smear it over the board.
Newcastle local Huon Oliver posted a photo of the dish on Instagram.
"Gourmet vegemite on toast. This is just ridiculous!" he captioned the photo. "Tasty but ridiculous."
"This is not on. This upsets me," one person commented. "Seriously??? Hahahaha by the time it gets to your table the toast will be cold … dry veg toast," wrote another.
"The toast would be well cold by then, the butter wouldn't melt. What a s**tfight," another person said.
Core Espresso's manager Emma Reid said there was a thoughtful reason behind why they served toast that way.
"If someone orders toast and they want Vegemite, we want to make sure it is presentable and that there is enough Vegemite on there. We don't skimp on Vegemite," she told news.com.au.
"Even though they're only ordering Vegemite on toast, we want our customers to know a little bit of care is being put into the dish. It's nice to put a nice quenelle on the plate," she said.
— with Rebecca Sullivan
