"Margaret thatcher the cum snatcher" is a nickname or term you give to someone who is always vigorously horny and craving sex for the pure enjoyment of seman.
Joe: I just had sex with Bianca.
Nick: why she's always trying to be "Margaret thatcher the cum snatcher."
Joe: true but I heard shell do anything for sex.
Nick: but still she "Margaret thatcher the cum snatcher."
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."