You try to warn Monica

You lean forward, putting your mouth directly next to Monica's ear.

"Uhh, Monica. I don't know if that's such a good idea..." you trail of, not wanting to say out loud that you've gotten so hard from her demonstration.

Monica's head swivels around so that she can address you from the side of her mouth. "John, are you only saying that because your cock is currently pushed up against my ass?" The smirk is evident now, and clearly thanks to your erection. She turns back to the class and speaks to her students.

"Ladies, I want you to pair off and take turns practicing against an attack from behind. I'll walk around with my lovely helper to make sure all of you are doing this properly."

Everyone began to separate themselves into pairs, and Monica turns to face you. She pulls you into an embrace and speaks softly to you, "John I can tell that this class hasn't been a complete waste for you." Her hands begin to rub your chest, slowly tracing their way down the curve of your body to your stomach. "At the very least, mini you sure seems to enjoy it."

With that, she slips a hand into the waistband of your shorts and reaches down to grasp your cock. Her eyes widen as it swells in her hand.

"I'm sure several of the girls in here would love to get a glimpse of this beautiful cock."

She grabbed the waistband of your pants, threw them down to your ankles, and stepped away.

"Ladies, if I may have your attention for one moment, John has something very special to show us."

Everyone stood in stunned silence for a brief moment, then a girl who looked to be a sophomore in college let out a low whistle before whispers began to run around the gym like wild fire.