Once I have swiped it, I just pass mine back to whoever i am with... it doesnt matter, as long as there is credit on it... This is from TFL Website :

"You can give your Oyster card to someone else"

If your Oyster only has pay as you go credit at adult rate on it you can let someone else use it, even if the card is registered in your name.

Not at the same time, no.

You can lend an Oyster card to somebody when you are not using it as per the rule Biff posted.

All this talk about Oysters is making me hornyyyyy

I like your optimism!