Goof: blue teddyboy jacket.
When Niven and Derek first meet, Derek is about six inches taller than Niven. However, Niven gives him his blue teddyboy jacket to wear, as he says he doesn't want it any more, but it looks too big even on Derek (he is shown turning the cuffs back).
Was this a genuine goof or was it meant to imply that the jacket wasn't Niven's, it was stolen?