It's like if someone offers you a beer. Bud Light or a strong IPA may not be to your taste, but saying "what do you have" sounds greedy unless they've offered a choice. A free beer is still a free beer. You either turn down the offer or you are grateful for the free beer. There are no other options.
"What kind is it? I don't want to deprive you of a beer if I won't enjoy it." There, done.
I had a colleague who'd ask: "What kind of beer? Heineken? That's no beer."
After a couple of those, everybody knows your taste :D