My response to the 'is he a good baby' question is 'no, he's awful, but we lost the receipt / the warranty is voided once you take them out of the packaging so we can't return him to the shop'.

Or 'where's your baby today?'. Response: (looking around frantically)... 'oh, sh*t, where did I leave him this time'.

But unfortunately most of the responses I get (even as a babywearing, publicly breastfeeding mum) are overwhelmingly nice so I don't get a chance to use any of my good comebacks.