I said in my post, there are a lot of cycling specific clothes that are not lycra tighties. I can understand if you're riding to work, then work/street clothes are your only choice. But most FG/SS folks I see are riding to hang out and scoot along with other FG/SS folks - in this case, it is for fun/sport/exercise/social reasons and casual cycling specific clothing is appropriate. When I see the choice of clothing used in this circumstance, I'm inclined to think that it's more for skinny jean fashion than for actual performance - because cycling clothing outperforms a pair of jeans/t-shirt anyday.

Wear whatever you want, but people discuss jean/t-shirt choice for riding apparel as if it's a practical solution for comfort, performance, etc. Jeans, t-shirt and hoodies suck for riding. They're thick, heavy, retain moisture and are not very wind resistant.