A slang term originally used by cattle herding cowboys to get their cattle to move faster. Elongated form of the the word yippee, which is used when a person is exuberantly happy about something. Has been used in numerous songs including Country Western, Hip Hop, and even Frank Sinatra used the term in a song. The term was made ultra-popular by actor Bruce Willis, who has used the term in each of his Die Hard film roles. In fact "yippeekyay mother fucker" has become his catch-phrase. Although we come across numerous different spellings of the word, we all understand it's meaning when we hear it.
Hans Gruber's reference to John McClane as a "cowboy" in Die Hard instigated McClane to use the phrase "yippeekyay motherfucker!" In other words "Yee- ha, let's get it on asshole."
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."