I commute to work by bicycle so every morning I change out of my cycling gear in one of the small changing rooms in the office.
Yesterday was a bit different, I was feeling particularly horny and as I walked down the corridor I could feel the beginnings of arousal - the pleasant tightness as my cock started to swell. I quickly entered the changing room and locked the door behind me. I stripped off my shorts and pulled my stiffening cock out of my underwear. I started stroking, watching myself in the mirror over the washbasin. I could hear people walking past outside. I found it exciting to be masturbating while everyone else nearby were going about their normal day.
The fire alarm went off! I panicked a bit and awkwardly stuffed my half-hard cock back into my underwear, then quickly pulled on my trousers. The alarm stopped and I remembered that today is when they test it!
I dropped my trousers and resumed masturbating. My cock quickly becoming fully erect as I stroked it while fondling my balls with my left hand. It didn't take me long before I trembled as I quietly orgasmed, carefully spurting my cum into the washbasin.
I cleaned up, finished getting changed, and started my day at the office relaxed and satisfied.