the condition of having an unhygienic mouth due to using your mouth to clean or pleasure ones own or other's lower regions (Down Under). Generally the Down Under Region would refer to feet or genitals or the floor. For a more specific phrase related to post-Cunnilingus mouth effect see: 'Mariana Trench mouth'

Oral-rectal gratification. When your partner kisses your rectal sphincter.

When God was making Australia, he started with the eastern side. After creating all of it's wonders, be couldn't be bothered making the western half, so he put a desert there and filled it with a heap of obnoxious, self-absorbed pricks.

aka Western Australia. The largest state in the world, on the West coast of Australia. Every other state hates us. We lose in the smarts competition. Hot girls. Hot beaches. Lot's of druggies and graffiti. Australia isn't the vacation destination you know it as people!
Can also be used in offence.

An airline for people who have don't like Qantas, so they fly with a carrier inferior service just to spite them

shithouse place nowhere near anything

the cheeks "down under," i.e., asscheeks