Having the type of mother he had, Sheldon was used to spankings. Granted, he got it way less than his siblings, but there had of course been the incident with the neighbour's cat; there had been no way of escaping a spanking after that.
He knew after research in his youth that it was seen as a disciplinary tactic that was frowned upon in modern America. Parents had been resocialized to believe that spanking was wrong.
But he, definitely, was not Penny's parent.
She had crossed the line for the final time. There were so many times he could dole out strikes, banish people and order them to take online courses. If one option seemed futile, a new option must be introduced to attempt to get a better result.
And that is what led Sheldon to grab Penny bu the front of her shorts and pull her down across his lap.
"Sheldon!" she protested, "What in the hell do you think you're doing?"
"You will not listen, so now you will have to learn the hard way!" Sheldon drawled, his father's words coming to him easily.
The first smack of his hand against her buttocks had her screaming in surprise and pain.
Yes, that's it.
He brought down his hand again, felt the stinging, watching her blonde hair flash about as she yelled at him.
"Never- sit - in- my- spot- again!" for each word, Penny got a slap.
She gasped, and her face turned to his, and her cheeks were red in embarrassment, "You're hitting me because I sat in your spot?"
"You brought this on yourself!" more of his father's words came to him, "You've been very, very bad!" those were purely his.
The tinge in Penny's cheeks got darker, and, to his surprise, her expression changed. He was very satisfied to see her expression turn remorseful. Her voice, when she spoke, was soft and piteous.
"I've been really bad, Sheldon," she said, "So bad. You should punish me some more."
He was a little shocked. Clearly she had seen the error of her ways. H e raised his hand, and brought it down on her backside. She twitched, gasped in shock.
"I'm not feeling it, Sheldon," she shook her head, "I've bad. Punish me harder."
Sheldon complied, smacking her harder. Part of his brain wondered if he should be taking instructions from her, when she was the one being disciplined. The thought was wiped clean when she wiggled in his lap. Sheldon had only ever achieved that sensation by himself.
"Harder, Sheldon. Teach me," she pleaded, looking back at him again. He was mesmerized by her face, the tinge to her cheeks. He hit her so hard she jerked in his lap, bringing back that familiar sensation.
He hit her, again and again, each time the sensation heightened. Then suddenly, Penny reached a hand between them and brushed her knuckles over his crotch as she unzipped her pants and he bucked up off the seat. Penny yanked down her shorts and panties, til Sheldon could see the fleshy cheeks of her ass, a little red because of his ministrations.
"Please," she whined and Sheldon was too far gone not to comply. She started to moan as he hit her sharply, wiggling so much that he was sure he would explode under her. She was moaning with every slap now, and some part of Sheldon's subconscious realised she was close, on the brink of something, and she would win if she got there without understanding the full consequences of her actions.
He grabbed her, pulled her up with him and stood her in front of him, taking pleasure in the look of utter shock on her face.
"What are you..."
"Take off all of your clothes," he growled deep in his throat, watching her look turn from shock to intrigue.

She complied, moving so slow that each stroke of her fingers against her skin was like a stroke along his cock.
"What are you going to do?" she asked, eyes wide.
"I am going to make sure you've learned to listen to me when I tell you what to do."
She gave him a look of disbelief, "What?"
"You will no longer talk unless I tell you to," he commanded, " Cup your breasts."
"Sheldon you..."
'No talking. Do it now."
Penny lifted her hands to her breasts and pulled them.
"No pulling."
Her eyes, which had fluttered closed, gave him a defiant look.
"No pulling until I say," he glared back at her til she backed down, "Now you may."
She moaned her thanks, taking full advantage of her breasts, rubbing her legs together to sate the ache between them. Sheldon reached forward and yanked her legs apart.
"No fair!" she yelled.
"I did not give you permission. When I do not give you permission to do something, you do not do it, understand?"
She nodded, "Yes Sheldon."
It made his cock twitch, "Say that again."
"Yes Sheldon."
"Do you want me to touch you?"
"Yes Sheldon, please."
"First you will have to learn the consequences of your actions. Now you realize you have been bad, do you not?"
"Yes, Sheldon. I've been soo bad!"
"How bad have you been?"
"I've thought about you," Penny confessed out of the blue, "I've thought about you in the shower. When I touch myself I imagine it's your hands rubbing my clit. I wish you could put that big cock inside me. I want you, Sheldon. I want you to punish me for being a bad girl."
Suddenly there was nothing Sheldon wanted more either.
"Why do you sit in my spot?" he asked.
"Because you're so damn sexy when your angry," she told him, "I love when you look angry, like you wanna punish me. It's all I can do not to whip out your cock and suck you off."
"Show me where you want me."
"Right here," Penny pushed her digits into herself, groaning as she slid her hands back and forth, "Right here, please, Sheldon!"
He moved forward, matching her fingers with his and capturing her lips. Penny jerked against him as both their fingers worked her into a frenzy. But then he pulled out, grabbed her wrist and pulled her finger out too, then back away from her lips. She screamed in frustration.
"Okay! I won't sit in your spot anymore, Sheldon! I won't drink your milk, I won't steal your t shirts, I won't breathe till you tell me to just fuck me, please! Fuck me hard!"
Sheldon smirked.
"On the floor," he demanded. Penny quickly dropped on her back and watched with impatience as Sheldon discarded his clothes one by one and folded them neatly. When he finally joined her, wasting no time in entering her, Penny groaned and arched into him gratefully.
"Thank you! Thank you, Sheldon, thank you!"
"You're welcome," he told her as he thrust into her hard, making her scream, "You have my permission to breathe. And you're welcome to the milk and t shirts. But never. Ever. Fucking. Sit. In. My. Spot."