Grandma Night 

A night in which friends gather together and get so crunk that after the partying, all they can physically do is sit on the couch like a grandma and rock back and forth.

Mike, Jordan, Zach, Robert, and Matt had a grandma night last night with a bottle of Vladimir. Zach passed out first. He was such a grandma.

Grandma Night by prohighfiver June 28, 2010

I had yer grandma last night 

It litterally means "I had sex with your grandmother last night."
It just removes the word 'sex' to make it shorter, like any other slang term.

Ryan: "Yo man, what were you doin' last night?"

Jack: "I had yer grandma last night"

Ryan: "What the hell man?! That's sick!"

I had yer grandma last night by jeNANANANANAA BATMAN! April 11, 2009