Katie meets me at the door wearing torn jeans, a plain white tee-shirt, and Doc Martins. She's not wearing any make-up, and she has her short hair slicked back.
"You look like a dyke," I say.
"It's an experiment," she says.
I hear voices from inside the apartment. Female voices.
"I thought it was just going to be the two of us this evening ...."
"Plans change."
I follow her in, feeling apprehensive. Sitting on the couch are three of her friends. They're all dressed butch too. They giggle when they see me.
"Take off your clothes," Katie says.
"What? Right here?"
"It's part of the experiment."
I strip down in front of them, growing increasingly self-conscious the more I expose. By the time I lower my boxer shorts, my face is bright red. They're all looking at my dangling cock. I resist the urge to cover myself with my hands.
"Look," one of the girls says, "He's getting hard."
"He likes showing off for us," Another one says, laughing.
Katie comes out of the back bedroom. She's wearing a big, black strap-on dildo and one latex glove. She's taken off her tee shirt so she's naked from the waist up. The sight of her bare tits makes me harder.
"Is this part of the experiment too?" I say.
"We're testing a hypothesis," she says, crossing over to me.
"Which is?"
"That I can make you come just by fucking you in the ass."
"Why are they here?"
"Witnesses. They said they wouldn't believe me unless they saw me do it."
Katie slides her gloved hand between my buttocks. I can feel the lube on her fingers. The tip of her index finger finds the tight pucker of my anus and begins to stroke, gently teasing me open. My cock is sticking straight out, the head a deep red. Slowly she works her finger in deeper. I moan, and shift my feet farther apart so it's easier for her to penetrate me.
The girls on the couch look like they're enjoying themselves.
"Wow dude," one of them says, "I never knew you were such a slut."
Katie's finger is all the way in. She hooks it, brushing my prostate, sending shivers down my spine. My cock twitches. I've never felt so embarrassed, or so aroused. I look at her pleadingly. She reaches up and pinches my left nipple hard enough to make me whimper.
"You are a slut, aren't you?" she says. "My dirty little slut."