An individual you really want to rail however the general consensus is that she is clapped. Furthermore, there are repercussions to the skeef such as your mates taking the piss out of you due to her conventionally being unattractive.
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."