It took forever for me to stop wearing cargo shorts to ride because I liked wearing underwear, but apparently, cargo shorts aren't very aerodynamic on the road. It does feel odd wearing underwear under tights but I guess its ok if they don't chafe or ride up. The only times I wish I'd worn underwear or a bikini botton with tights are when I'm riding on a muddy, wet trail and there's grit getting into my tights and heading southwards. That's when I start getting paranoid about grit and UTI. *Shudder*