If the person who is buying the cake wants tog et a certain flavor, fine.
And the most gracious choice *might* be the honorees favorite flavor, but if it's a communal b'day, then "a flavor that everyone can eat" is fine--because it's not a one-person cake.
But it's sort of ungracious to say, "you get to pick, but you don't get to pick your favorite flavor."
I don't understand why anyone would ask someone what they wanted for their birthday and then deny them.
Yeah, if you're going to ask, be prepared for the answer.