shack

An unexpected sleepover at someone else's place. Sex may or may not happen. The term shacking does not apply to staying the night expectedly, when you have your own change of clothes and a toothbrush. A shack often involves borrowing or stealing the guy's clothes for the walk of shame the morning after, thus the term "shacker outfit."

"Yeah I shacked at his place last night after Paddy's."
"Nicole didn't come home last night, she shacked at Ryan's."