Bloke 1: Me and the boys are gonna go on a road trip, you wanna come ?
Bloke 2: Nah, sack.
(Alternatively, the word can be used as an adjective.)
Bloke 1: did you wanna come and
rob the 7/11 down the
road tonight ?
Bloke 2: Nah, my cars getting serviced, it’s a bit of a sack to
walk there.