When two people are engaged in sex, one person, usually the male, inserts their finger in the anal cavity of their partner, and proceeds to wipe particles of feces on the upper lip of their mate.
My girlfriend and I were having sex last night, and right after I had an orgasm I gave her a dirty sanchez.
To take something small, that doesn't quite qualify as a theft. Probably from the Danish "skæv" or the Dutch "scheef", both of which are pronounced similarly, meaning "askew, or not quite right'. To change an item's ownership without permission, but only something small and of little worth.
"I skeefed an apple off the neighbor's tree." "I skeefed some chips outta your bag when you looked away." "Don't skeef my chair when I go to the bathroom."