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2 definitions by Panic! InMyPants

 
1.
An acronym: Bare Back Ass To Mouth.

Slang mainly in prostitution circles and used to describe what a particular call girl will do. In this case Anal sex without the use of a condom followed immediatly by oral sex.
An actual craigslist ad:

Let this young lady charm your heart with all her special talents. A brunette with blue eyes, who could resist such a beauty. Availiable appointments now.

$800/hr- bbatm
$600/hr- bb
$450/hr- greek
$300/hr- full service
by Panic! InMyPants November 15, 2006
 
2.
When a ring is worn on your thumb it advertises your willingness to engage in anal sex. Like white pants it transcends the boundaries of gender and sexual orientation.
Kevin: "Hey Lisa May! Whats with your thumb ring?"
Lisa: "I'm hoping to find a willing guy at the bar to give bbatm"
by Panic! InMyPants September 17, 2008