The West Lothian celebrity appeared on the American YouTube channel Fine Brothers Entertainment (FBE) to give his opinion on the accuracy of movie character's impersonation of Scottish accents in movies.
During the interview, Mr Capaldi jokingly said: "This should be easy, because I am from Scotland," before watching clips of Fat B*****d in the Austin Powers film series, admitting he used to do impressions of the character at parties as a four-year-old.
He said: "I used to go: 'Look at my sexy body'. Also it's strange that in real life, I became a fat bastard.
"I mean, if you look at Fat Bastard and then you look at me, doesn't look too dissimilar."
He further informed the viewers the correct name isn't Fat Bastard, but "fat baster, if he's Scottish."
Although he was kind to Mike Myer's impression of a Scotsman, giving it a point for accuracy, he was less benevolent of others.
In the video on the channel, which has over 32 million subscribers, the 22-year-old star was impatient with Mel Gibson's Braveheart 'freedom' speech, saying: "Let's just go get killed and kill some people."
He added: "Don't shout freedom at Scottish people, it's very annoying."
When asked to comment on the accent, he said: "It's just Mel Gibson doing a Scottish accent."
"It's not that bad, it's just not the best, so I'll say not accurate, because I feel like I should say at least one isn't."
The Someone You Loved singer went on to discuss James Doohan's Scotty from the original Star Trek, The Simpsons' Groundskeeper Willie and Mike Myer's Shrek.
He commented: "I didn't even know Shrek had a Scottish accent, I just thought that's how ogres sounded!"
But he admitted parts of it did sound accurate, concluding: "I think Shrek is good, good guy, good accent."