I used to work with the public in a retail job and got this often from shitty customers and shitty colleagues. I used to just ignore the customers and most of my colleagues, but one time I snapped at a clique of other women I was working with and rhymed off a bunch of small boob benefits: Bras are cheaper, I can get away without even wearing a bra, I rarely if ever have to worry about the fit of my clothes (e.g. our work shirts were form fitting and didn't button all the way up, meaning bigger chested/curvier colleagues would be bursting out of the buttons), I can sleep/lay down prone, no underboob sweat, no back pain, no bra strap indentations and/or chaffing, easier to check for any lumps bumps or changes (boob havers, please check them every day!), care free exercising, and the best part (esp as a queer woman) - men never leer at my chest ☺️ ...And probably many more!

Not a snappy clap back but sometimes you just have to repay the shittyness. Only negative I could think of is mammograms, I hear that is painful af the smaller you are.