You'll never hear Matthew McConaughey answer to 'Matt' or 'Matty' - and there's a very good reason.
He's too scared of the consequences.
"I answered to Matt one time when I was in kindergarten, when my Mum was my teacher," the 47-year-old Hollywood star told Nova FM's Fitzy and Wippa show on Monday morning.
"My buddy goes, 'Hey Matt! Wanna play on the monkey bars?' and I said 'Yeah' and ran to the monkey bars ... and next thing I know I feel a hand on my shoulder pull me back and body slam me to the ground - and it was my mother."
Turns out, she wasn't impressed by the friendly nickname.
"She says to me 'What's your name?' and I said 'Matthew ...' and she goes 'Why did you answer to Matt?' and I said, 'I don't know, I knew he was talking to me!' and she said 'Don't you ever answer to that again - I named you Matthew on purpose'."
The severity of her response appears to have scarred the father-of-three for life.
"So if anyone calls me 'Matt' I know they either don't know me well or they're jacking with me," McConaughey told the radio hosts, before admitting he's still scared of his mum.
"She's 84, but she's still spry."
The star, who lends his voice to a koala character in new animation movie Sing, also reminisced about his time living in Australia.
"Two weeks out of high school, I came down there [to Australia] for a full year. I lived in a little town called Warnervale ... population 305," he recalled.
"And I got introduced to five-day cricket matches, where you drink beer, snooze, pass out, then wake up and there's not another wicket gone."
Earlier this year, McConaughey opened up to news.com.au after copping a fair bit of flak over the decision to cast him as an Australian character.
"Australians are not offended that I played a koala bear! Australians don't get offended by things like that!" he insisted.
"You guys are no-frills. I lived over there for a year, I've made three films there, and I know Australians well enough to know they're not offended ... I worked 11 different odd jobs the year I lived in Australia."
The cast includes Reese Witherspoon, Scarlett Johansson, John C. Reilly, and Seth MacFarlane, and follows the story of a koala, Buster Moon (McConaughey), an entrepreneur trying to stop his theatre from being shut down.
Sing will be in cinemas on Boxing Day.