We have a casual policy, and if I wear jeans (almost every day), I'm always commando.It's just more comfortable for me.
However, I have several different fits of jeans (work, weekend, gay bar, etc.). I go to the gym early a couple of mornings a week before work, and leave the house in my gym clothes, with my work clothes in my gym bag. There have been those days when with my early morning sleepiness, I've packed the weekend jeans by mistake. Then I have to arrange things a bit, and try to make the best of it, when dressing after working out.
But there was one morning when I not only packed the wrong jeans, but was running late for work and didn't notice when I dressed in the locker room. I only became aware when I walked up to the office coffee station, and this woman's jaw dropped wide open as her wide eyes locked on my crotch. Honestly, I wasn't showing that much bulge...