When a woman gives two consecutive blow jobs to two different males, and the ejaculate from the first male is still in her mouth upon the second act of fellatio.
I caught Theresa cumdoubling at the work holiday party, Pete was pissed that he was second.
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."