anal erection 

When you get aroused so much that your ass cheeks automatically clench and can't stop!

Man: Nice Ass!
Woman: Thanks! I Shaved It Yesterday.
*Anal Erection Begins*

anal erection by AlexPower October 9, 2008

Anal Erection 

The act of shoving a flaccid penis into the ass of someone of any gender, and getting an erection with the penis already inside of the ass.

Guy: Hey babe, wanna do anal?
Girl: I'm afraid it will hurt too much...
Guy: We can try an anal erection.

Anal Erection by Old_Ben January 4, 2018