Crest Pro-Health > Listerine but anyways on the back it says 'If more than used for rinsing is accidentally swallowed contact poison control center immediately' What kind of idiot would drink mouthwash out of the bottle? Otherwise swallowing some of what you use to rinse is not harmful.
Your initial response was about not rinsing - hence my reaction. Obviously you aren't supposed to drink the stuff. But there's no harm in not rinsing.
You can actually get drunk off of drinking mouthwash. Listerine is 26.9% abv. They denature the alcohol though, so you may very well get ill from it if you drink enough.