12th base 

To defy the laws of physics whilst engaging in sexual intercourse.
A common example is to have sex listed as the 'Bat Position' in the karma sutra, and that is to have sexual intercourse on the ceiling.

I went to 12th base last night and i got such a rush to my head.

12th base by Rhodri Griffiths July 30, 2008

12th base 

A sexual act including a saddle and/or table tennis paddle

guy 1: we got so far last night
guy 2: what base
guy 1: 12th base
guy 2: Woah!!! how did u get a saddle into her car

12th base by Super Robo Boogie Bot II October 10, 2008

12th base 

When your girlfriend removes her glass eye and you prodceed to insert your penis inside the hole and fuck her.

Guy 1: "Dude we got to 12th base I don't deserve to live anymore."
Guy 2: "shit bro I'll get my bat."

12th base by Shaniquaobamaniqua September 17, 2013

12th base 

Fucking a chick so hard that she dies.

Man 1: Ah shittt man, I fucked Cindy so hard, I got to 12th base!
Man 2: FUCK! Where is the mangled-sexfilled-corpse?
Man 1: In my car where I left her...
Man 2: I say, go for 13th base
Man 1: Ahh, wanna munt her with me?
Man 2: YEAAHHHH, I'll jump.

12th base by manyperson August 10, 2009

12th base 

Giving foot and or boob jobs with 2 or more people.

Dude, last night i got to 12th base with this hot chick and her twin sister!

12th base by Klunckmonkey June 11, 2006