Tell him you're going to the restroom

You decline his offer, "Thanks, but I really need to visit the restroom first."

After getting out of your chair, you head towards a back hallway where the bar's restrooms are located. You walk past a group of people standing by the ladies room, but as you reach out your arm to push open the door one of the women stops you.

"Sorry, there's a line here for the bathroom."

"Oh, I'm really sorry," you apologize.

A solid dozen people are standing in the line outside the restroom you realize. Closing time is nearing and apparently a lot of people are visiting the restroom before leaving.