Birthday Girl

"Johnny, since Mom… Oh shit!"
I hopped back out of the guest room that I'd just barged into. I'd accidentally caught him doing the… What was that cute term Becky used for stroking it? Oh yeah, the five-knuckle shuffle. I lifted my hand to my mouth and giggled. "Sorry, Johnny!" I said loud enough to be heard through the door.
"Dammit Tammy. You know you don't just barge into someone's room. Didn't anyone ever teach you to knock before you come in?" Johnny's voice seemed shaky.
I bit my lip. "I told you I was sorry."
This was the opportunity I'd been looking for, so I was going to follow it for all it was worth. "Can I come in now?"
"I guess."
I eased the door open. Biting my lip to keep from smirking, I sashayed up to the bed and sat at the foot. He sat at the top against the headboard, his arms wrapped around his knees, which were covered by a sheet. He's trying to hide his woody.
"Happy Birthday by the way."
"Thank you." I snickered.
"What's so funny?"
I shrugged and wiggled my underdeveloped butt as the image of his erection embedded itself in my innocent, but devious mind.
When I didn't say anything, Johnny asked, "What do you want to do for your birthday?"
I wasn't sure why, but it was getting warm between my legs. "Ah, I thought since mom and your dad went to mom's twenty year reunion and sorta left you in charge, maybe, since it's my birthday, Becky could spend the night."
His gaze glued to my chest. "Sounds good to me, go ahead."
Being a late bloomer and having relatively flat boobs, I rarely wore a bra—like now. I glanced down at my belly shirt and—sure enough—my nips were hard.
He probably thought I'd thank him and leave. But I didn't.
My groin started to warm up at the thought of what I hoped to do. God, I wanted to touch myself. I moved both of my skinny legs up onto the bed and crossed them Indian Style. "I-eeya…there's something else I'd like to do for my birthday now that I'm 18."
His eyebrows elevated as his head tilted. "I'm listening."
Brazenly, I reached between my legs and rubbed my bud through my shorts. "Well, if I may be blunt, seeing you wanking-off to Penthouse has my pulse rate in the stratosphere and my you know what, warmer than Old Faithful."
He turned a pretty shade of pink. "I wasn't wanking-off to Penthouse. And I don't know what 'what' is."
"Yes, you were...