Nothing takes the sting out of being swept in the playoffs like a Justin Bieber concert ... so says NBA superstar Andre Drummond.
The Detroit Pistons star was at LAX -- proudly displaying his VIP backstage pass to Bieber on his backpack from his concert in Michigan on Monday night ... one day after the Pistons were eliminated.
"He's a cool dude," Drummond told us.
AD also says Bieber put on one helluva show -- but it wasn't perfect ... he's still got some room to grow.
As for the rest of Andre's off-season plans -- don't worry Detroit, Drummond says he'll come back even STRONGER next season.