You okay?

For a while now, I've been wanting to share some ridiculous British slang and phrasing. So here's one that I encounter every day and it never ceases to cause me discomfort. In the US, if someone asks another person if s/he is "okay" - as in, Are you OK? - the connotation is one of concern because you probably look NOT OKAY. Like, worried, like you might puke, uncomfortable, hungover, maybe your mascara is smudged because you just woke up from a nap at your desk at work or you have a piece of toilet paper hanging out from your skirt (none of these things have happened to me, PS, I'm just being creative). But here in London, if someone says "You OK?" to me, THEY ARE JUST SAYING HI. It's the British equivalent to "What's up". And because that is its meaning, the acceptable responses are "OK, you?", "I'm OK, you OK?", or as Mark put it to me when I queried him on this topic - "A simple nod of the head will suffice". I'm still trying to get the hang of, as I'm rushing into work (late) in the morning, responding to "You OK?" with "You OK?" instead of a huffing explanation for oversleeping.