You would think 1OAK would turn away unstable patrons, but if the customer is good for business all bets are off ... because they let Amanda Bynes party there.

Amanda hit up the West Hollywood nightclub Thursday night with a flower-crowned friend.  It's impossible to believe people who run the club don't know she's been in a mental facility and is extremely unstable, but hey, everyone's along for the ride to see what Amanda does inside.

Check out all the people watching as Amanda gets in the car.  It's amazing the club didn't sell tickets.