When I was in high school and college, I was a compulsive exhibitionist and public masturbator. One time, freshman year, I remember walking around campus about 10 at night, looking for a chance to expose myself. I walked by the library. Around the back it was quiet, and I saw a study room with two cute girls in it, a blonde and a brunette, sitting at a table, facing outside. The grounds were dark, but light was pouring out from the full length windows. I took my shorts and top off so I was naked. Then I jumped in front of the window. One girl saw me, gave a shocked look then a big smile, and nudged her friend to look. They both looked and laughed. That got me so horny, I started to masturbate!
They looked shocked! One kept staring and laughing, the other just stared, her eyes fixed on my erect cock. Finally, I came all over the place, including right on the glass window!
The blonde was laughing hysterically, but the brunette suddenly got angry, banged on the window and hollered 'go away pervert!' I got my shorts on quick and ran like crazy! I masturbated outside and in that library numerous times after that, but never saw them again.