I think it's an American saying meaning 'wake me up', as an expression of surprise at something that's been said or that's been done, but with a sarcastic edge to it. It can also mean that the person hasn't got a clue what the other speakers are talking about.
Heavy metal kids and nerds sometimes say it when they're out of their depth in a sexy situation...a bit like saying 'hey pussycat...grrrr!' - or then again to be sarcastic to someone unattractive.
That's my interpretation anyway, there are prob. loads of other instances where people would use that expression to lighten up a conversation.