It was just sitting there, that exposed lower back. The small gap between her blouse and her jeans coyly flashed me her flawless skin, smooth as a baby's bottom and fair as freshly milked cream. Should I do it? I'm gonna do it.

Slyly, I slipped my finger under the back of her white panties and pressed the spot below her spine just where her asscrack began.

"Cut that out, it tickles," Jennifer said, jabbing me in the ribs.

My girlfriend Jennifer and I were at our Friday night tuition class. Up front, Mr Chen was droning on and on about factorization or something. Who cares. I had been trying to 'activate' my girlfriend for nearly a month with absolutely no success.

I was frustrated as well as confused. Was it all a coincidence? Was Vanessa merely naturally horny when she and I got down and dirty below the mango tree at the side of the koi pond last month?

Behind me, I heard a chuckle. I turned around to see Alicia, Evon, and Stella grinning at me. They had caught me slipping my naughty fingers behind my girlfriend's jeans. I smiled back sheepishly. I wondered if I could try 'activating' them as well, maybe I needed a bigger pool of test subjects.

Then I shook my head. What was I thinking? Alicia, Evon, and Stella were all attached. To my friends no less. Jeez. Having a little bit of power sure goes right up in my head. Besides, it's not like I can just waltz up to them and play grabsies with their butts. Jennifer will kill me.

But if I could, oh man. The thought of the three girls struggling with each other to play with my cock surfaced in my mind and tormented me. Damn. I had to calm myself down. Think of something unappealing.

I thought of Grandpa, thinking it would do the trick. To my surprise and greatest of horror, I became aroused. Fuck? What's going on? Am I now gay for Grandpa? Calm down Johnny, I said to myself. You've faced this before.

It was true. I experienced this back at Grandpa's house during the Chinese New Year. It was after the craziness with Vanessa, as I was wheeling Grandpa back into the house. For some reason, I was getting aroused again.

Back then, I just brushed it off as a weird side effect from my hot session with Vanessa earlier. But what if it wasn't? What if it was because of Grandpa? Does Grandpa arouse me? But wait. It was Grandpa who first 'activated' me. Could it be because of that?

And if that is the case, I activated Vanessa. Oh shit. But the more I thought about it, the more it made sense. Also, Grandpa, me, and Vanessa are the only three people I know who have this effect right now. Okay, maybe not Grandpa, because I doubt he could reach down his back to poke his weak spot given his condition, and I'm pretty sure no one is interested in giving him a butt-crack rub.

But Grandpa knew about the weak spot and now I and Vanessa are affected by it. I've tried multiple times, and it didn't work on Jennifer. The only common denominator between Grandpa, Vanessa, and me is that we are family.

Oh, this is great. This is just fucking great. I finally learned the ultimate skill worth pursuing and now I figure out I can only use it on family members. Clearly, the path down this road will only lead to more incest. What rotten luck.

"Wei, what's wrong with you la?" Jennifer asked.

I turned and blinked at her, "Uh. Sorry. A lot on my mind."

Under the long desk we shared, she placed her hand on the front of my pants and rubbed me affectionately. "Horny is it?", she whispered. I nodded happily.

Jennifer: I knew it. You've been so horny lately. Can't stop touching my butt

Me: Hahaha. Sorry babe. You know I find you irresistible

She smiled and gave me a sultry look. "Want me to suck you later?" She asked.

Me: What? Here?

Jennifer: No la, in toilet lor

Me: Hehe. You're so good to me

Jennifer: Serves you right for being so cute

Ah. Bliss. Makes me wonder if I need to find Jennifer's weak spot after all. This girl really knows how to pamper me.

My tuition class ended at 10pm. Jennifer and I were in the restroom, sharing a cubicle by 10.03pm. I immediately took her in my arms, and we shared a tender kiss. After we heated each other up a little, Jennifer took a step back and sat down on the closed toilet, smiling mischievously.

I wasted no time unbuckling my cargo shorts and dropping my boxers. She grinned when she saw how hard I was. Gently, she took my throbbing dick in her hands and guided me closer to her. She stroked me for a minute before popping my cock in her mouth.

Wow, I'm loving it. As Jennifer sucked and toyed with my cock with her tongue, my phone sounded a message alert. Dammit, my mom can't be here to fetch me already!

I reluctantly stopped my girlfriend long enough to stoop down and retrieve my phone from my pants. She immediately resumed sucking on my meat while I checked my messages. There was a new message, but it wasn't from mom. It was from Mark, my older brother.

Mark: Woi, where u? Faster come down, I'm in a hurry

Dammit, Mark must have had plans tonight so Mommy must have told him to fetch me on the way since we only have one car left. Daddy has the SUV but he took it with him on his business trip. Meanwhile, Jen kept sucking and bobbing, her lips going back and forth, back and forth on my cock.

"Oh shit, I love you, baby..." I whispered.

"Mmmm," she went as she looked up at me.

Panting slightly, I typed out a reply to Mark.

Me: I'm in the restroom, need to drop a big hot load

I can't help being cheeky about it.

Mark: Shit! Hurry up la, I'm going to be late because of you

Me: Ok, Ok, I'm coming, I'm coming...

And I really was too. Grunting softly, I ejaculated copiously into my girlfriend's sweet mouth. A soft gurgle escaped her lips as her cheeks swelled to accommodate each hefty spurt of my healthy seed.

When it was over, she pulled back, looking flustered. Her cheeks were puffed up. She quickly got up and lifted the toilet seat cover before bending over and spitting an enormous gob of white sperm down the toilet.

"My god," she said. "You came so much."

"Cause you were so hot baby," I replied.

Inwardly, I wished she would swallow it. Vanessa swallowed it though. Vanessa swallowed a whole lot of it. Oh, shit, I'm getting hard again.

"Good to go?" Jennifer asked, beaming at me.

"Sure babe, you're the best," I told her and kissed her on her cheek.

After pulling my pants up, I let Jennifer out of the bathroom first before making my own exit after a while.