Like others, it was when I hit puberty and realised that my package was pathetic compared to other guys. It's average when erect (just shy of 6"
but really tiny in its normal state. Nowadays I find it a real turn on to have a small penis, and one of the reasons I love going to male saunas is the embarrassment of flaunting my little cock in front of other guys with thick long cocks. I find most cocks a turn on, small as well as large.