She asked me why didn't I find a more beautiful girl. What to reply to such a self disqualifyer? Funny, preferrably..

You don't answer that literally, obviously. You don't say "Because you were the best I could find at the moment." And you also don't compliment her and come across as needy and say "Oh c'mon, you are gorgeous!"

What I would do is start speaking in generalities, that way it you aren't negging her nor are you complimenting her. Say something like "All women are beautiful in their own way. I personally don't judge people based on looks because beauty is common, but a good personality is rare."

That way you are showing that you are this cool, non-judgmental person, and yet still aren't answering her question since it could be a shit test.

_________________
“Nothing is impossible, the word itself says 'I'm possible'!” ~Audrey Hepburn