Ok, so I have heard these expressions on the forum numerous times, but I must admit I am at a loss as to the meaning, history, or origin of either phrase. I Can't say I have ever heard a Scot or Canadian use either phrase, but they seem to be very popular with the US members. Can someone fill me in on these?

By the way, I am not taking the piss, just curious as I haven't really heard these in person before.