I used to get that one on occasion. Depending on when they asked i.e. when I'm training, middle of a set, outside of the gym, and how they asked, i.e. respectful, truly inquisitive, or smart ass, I would give them this answer,
" I would start with plastic surgery to fix the most obvious differnces, and then I would workout and diet".
I know, not to cool, I would not reply in the same matter today but it does tend to end the conversation pretty quickly.
Also someone earlier said the "fat guys" never want to really do what it takes to get lean and the lean guys never really want to do what it takes to get big. That is so true. I went on a 8 year bulking phase one time.
When I work out in Italy on occasion most guys in the gym are smaller and weaker but in general much more cut. I kind of feel smug because of my size and strength and I think they feel smug because of their leaness. I think we both would like to achieve a little of what comes easy to the other.
Pekkerwood