Zuff is a very sexually charged word. It has no specific meaning but is instead an expression of agreement with or being turned on by a sexual statement. It takes the place of phrases like "oh yesssssss", "oh baby", "take me now", "that makes me so hot", and the like. It should always be said in a lusty, animal, manner. It only takes on a serious context when used between lovers at a very sexual moment.
Take the following exchange for example:
hamsty winks at masu
herbman: its all you
masukomi: zuff
When filtered through an appropriately depraved mind it would roughly translate to:
hamsty winks at masu with a sultry grin
herbman: I want your body.
masukomi: Come and take me now. I want you both, right now.