To have sex with another's mom, or a group of moms in a particularly disrespectful way. If your mom gets sloinked, no one is buying her dinner afterwards. It's traditional to pee on said moms kids afterwards to complete the ritual.
"yo bro, I just got back from sloinking you mom in the backseat of my Subaru. Didn't even give her a ride home"
Sex while travelling or living in Greece, Crete, or the Mykonos Islands.
While on vacation in Greece, we had multiple rounds of oral, vaginal and anal stoinkos daily. The locals told us that anal stoinkos is a national pastime.