The act of having intercourse with a girl who is so thin that the pressure causes an outward bulge to appear from her stomach.
"That chick I banged was so slim, I thought The Alien was gunna pop out of her and attack me!"
by Andrew April 09, 2007
A sexual maneuver, in which a female/male is in the process of giving oral pleasure, and has to almost unhinge her jaw in order to her her lips around the males penis.
Dude the other night my girlfriend had to do the alien in order to get my dick in her mouth!
by mrrwbrown November 27, 2013