Gallic
A Gallic shrug is when a French person just casually shrugs like they're telling you to go to hell and they don't care if you end up dead.
'It's not my problem,' he said, shrugging like he had just won the lottery.
She just shrugged and walked away, leaving me to deal with the mess.
He shrugged, looked at me, and said, 'You're on your own.'