Moments of vulnerability from a coworker at work whom I never thought of as a member of the opposite sex before. Napping in the passenger seat of a sales car, getting completely soaked during an unexpected downpour while making external visits, or being drunk and knocked out, among other situations. Catching a glimpse of cleavage or a panty flash, not that I wanted to see it, but I thought, "Wow, that guy has some decent boobs after all..." and then suddenly I'm "uh-oh," getting an erection. "Oh, forget it," I just let my dick take over and came!
