Mum Hester Greeff asked her 20-year-old son Ruan Becker to make her a coffee while he was getting breakfast at home in Johannesburg, South Africa, before he had to leave for work last week (14 April).
But Ruan, a hospital authorisation clerk, rejected her request - prompting the 41-year-old housewife to hatch a plan to get even.
Hester teamed up with her boyfriend Jannie Botha, 44, to transform herself into IT villain Pennywise, using an old fancy dress outfit and makeup.
Hester then climbed into the bin around the back of their home to lie in wait for her son, who had absolutely no idea of the horror that awaited him.
Jannie asked Ruan to take the rubbish out before he left for work, which this time was a task he dutifully accepted.
However, as he lifted the lid to place the trash in the bin, Ruan was confronted with his greatest fear.
Footage shows how the poor lad screamed, dropped the bin bag and ran as fast as he could as soon as he saw the clown - who, unbeknownst to him, was just his mum.
The amusing moment went viral on social media after the video clip was shared on Facebook, where it's been viewed more than 1.7 million times.
While some people reckon they'll have to give it a go themselves, others have a little more sympathy for Ruan, saying they'd 'cry their eyes out'.
Ruan said: "I was so scared, I didn't know what to do. I absolutely hate clowns, I have been ever since I watched IT when I was nine years old.
"I had no idea they had planned anything so it was a complete shock. I didn't see it coming as this is completely out of character for my mum.
"We never prank each other but this started with me not making her a cup of coffee. I could not believe it.
"The first time I watched IT, I had a nightmare the same night. The next time I went to a funfair I was chased by a clown for a joke and I just started screaming.
"I haven't planned anything yet, but I will get my mum back."
Featured Image Credit: Kennedy News