No-one likes being mistaken for someone else - especially if that someone else has been their sworn rival for more than a century.
So when Guns N' Roses' announcer yelled "Sydney" just before they walked on stage in Melbourne, the band were met with a chorus of boos.
And to make matters worse, the veteran rockers weren't even on time.
Luckily, it seems they made up for it with a rousing concert - and a swiftly issued apology on social media.
"Melbourne!" the band - which had just completed two nights in Sydney - posted on Twitter.
"Accidentally after 30 years McBob made an error, we're truly sorry. Thank you for coming out tonight!"
Luckily, guitar technician McBob, who has been introducing the group on stages around the world during their Not In This Lifetime tour, was quickly forgiven by fans for his momentary slip up.
One follower replied to the post with: "One mistake every 30 years... Reasonable."
Getting it wrong
Turns out, Guns N' Roses aren't the only ones to get a little confused on their exact location.
- Britney Spears did not win any extra applause for confusing Manchester with London in 2009
- Bruce Springsteen yelled out "Party noises, Pittsburgh" in March 2016, only to realise he was actually in Cleveland
- Usher managed to mix up Manchester with Maidstone, in Kent, at Radio One's Big Weekend back in 2008
- Robbie Williams went one better, and confused which country he was in back in 2015 - yelling out "Zagreb", Croatia, instead of Belgrade, Serbia
Sydney and Melbourne, Australia's two largest cities, have had a long-running rivalry dating back to gripes over trade during colonial times.
Today they feud over which is the better city, with grudges mainly played out on sports pitches.