Mexican Periscope 

The act of spreading a woman's anus open with your thumbs, then peering into it like a periscope. Technically could be performed on anyone, by anyone, but in the original example it was a man performing the act on a woman.

Originated from a post on the Tosh.0 blog.

Man, that chick is crazy. She asked me to give her a Mexican Periscope!

Mexican Periscope by TexasCracker April 11, 2013