This reads like a joke question, I know, but I actually mean it.
Are you supposed to answer this sort of suggestive question with honesty? Or is this generally meant to be answered in coy and or affirmation? Because I don’t want to ruin the mood but I also don’t want to unwittingly spoil her expectations. (FYI, I’m average sized.)
I cannot imagine asking a guy his size. That is rude as heck.
If you have to answer “big enough” or “haven’t had any complaints” seems reasonable though honestly I’m having trouble putting myself into the mindset of someone who would inquire.