With summer also came my birthday and it would turn out to be a birthday I'll never forget. Karen woke me up at one minute after midnight, the actual time of my birth, with a kiss. I wrapped my hand around the back of her neck and kissed her back. Her hands ran down my chest and mine found her small round breasts. We made out for a little while being as quiet as possible before she broke free and handed me a present. She told me it was a secret present and that I had to open it right then. I opened the carton and pulled out a pair of sexy nylon panties in black with a floral pattern on them. I looked quizzically up at Karen who just smiled at me and said there was a card too. I looked in the carton again and there was indeed a card. I took it out and opened it. It read: "I dare you to wear these all day!!"
My first thought was: sure I can wear them under my boxers and no one will ever know but that plan went out the window when Karen specified with a giggle and that special smile she had - like poison come to dinner - that I was to wear no other underwear than those panties. She added that if I completed the dare there would be a reward at the end of the day. She was of course talking about sex. That much was obvious but since we already spent most of the last three weeks fucking each other's brains out and discovering new ways to do. So I knew it must be something more than just sex she had in mind.
Oddly enough I don't remember hesitating. I sat up in my bed, pulled off my pj pants, slipped the panties on and stood up to pose for Karen in them. The fabric and fit of the panties were very different to what I was used to and the touch of the soft thin nylon made my cock go rock hard in seconds, not to mention the taboo idea of wearing female underwear. My cock quickly outgrew the panties and the head peeked out above the waistband. Karen gently touched the tip of my cockhead before leaning in to give it a kiss. I nearly came right then and there. She glanced at the alarm clock and told me that at twelve minutes past midnight the next day I could take them off and the dare would be completed.
She gave me a good night kiss and crawled back under her blanket. I was so aroused I could barely sleep. My erection didn't go down and I didn't dare touch myself for fear of staining the panties and then having to walk around all day with dried cum in my underwear. Karen appeared to be sleeping soundly but before I finally dozed off I heard a faint moan coming from her mattress. She was probably touching herself, whether in her sleep or not I don't know.
When the alarm clock rang I still had a full erection and a beginning pain in my testicles. That was when I realize the day would be one long hell of erotic stimulation. I went into the bathroom to shower and use the time in there to rub off a quickie. So I locked the door and got out of my pjs and the panties. It felt so good to let my cock out of the tight confines but the pain in my testicles grew worse. I wondered if Karen was aware of this side effect of her birthday present. She probably was. It was just like her to pull a thing like that. She was pure evil brilliance when she wanted to be.
I had just stepped into the shower and started rubbing my cockhead with a soft sponge when there was a knock on the door. It was Karen who said she needed to pee really bad and if I didn't let her in she'd wet herself. I covered myself with a towel and opened the door. Karen rushed in holding her hands at her crotch as if she really needed to pee real badly. I closed the door behind her and she locked it. She pushed me up against the bathroom wall and kissed me while wiggling out of her pjs. Once she was naked she grabbed my now throbbing cock and sat down on the toilet. She blew me while she pissed. It took maybe 30 seconds for me to unload in her mouth. I was just that aroused from having worn the panties all night. Afterwards I wiped her clean with my tongue, she put her pjs back on and slipped out with a giggle.