I've drunk Listerine before. It's awful. I've known people who have drunk vanilla extract. I've bought cooking wine (like the stuff near the olive oil and vinegar in the grocery store) and drunk that. You don't need an ID card and can buy it anytime, even when blue laws prohibit alcohol sales.
I would have alcohol free mouthwash around. I can't imagine swishing my mouth with alcohol. Your guest may feel like they'd be inconveniencing you by asking for something special. Best or err on the side of caution.