Whisky woes

Graham has an expensive bottle of whisky in the cupboard, and I have an expensive bottle of brandy. Graham poured himself one of his whiskies and offered me one.
When I’d had finished it:

Me: Would you like one of my brandies?
Graham: Oh, I didn’t offer you a whisky just for a brandy in return.
Me, turning away to get on with something: Oh good.
Graham: !!!!