The coach drives Kevin home, and gave him some of his bigger clothes, which were baggy on him but would look really tight on Kevin. They didn't talk that much after he saw his son, but it was clearly because the coach felt really intimidated. His alpha male authority was at risk with his much bigger son.
Kevin was changing, and he couldn't help but flex his new muscles that filled his dad's clothes to their limits.. His dad would never dare to treat him or his mother bad again. There should be an explanation for his growth, but he was blinded by power rushing through his systems.
The coach took out the milk gallon from the fridge, pured it in the blender and added a lot of his protein suplements to it. He mixed everything and started downing it.
"That kid can't beat me. He must respect me, so I must be the big man of the house".
The coach headed to the basement, and started benching the heaviest weights he had. Tons of heavy bicep curls later, he downed another drink of the shake. Some push ups and chin ups later, he finishes the super shake. He started feeling really weird, in a good way. His tank top started feeling tighter than usual, and he couldn't help but notice a bigger bulge in his pants.
The coach burps loudly, and his clothes explode. His muscle fibers, already big, became three times their size. He looked like his son now.
"What the fuck? So that was it! The milk! Kevin grew huge because of it. He drank a glass of it... But he was a fat loser, and he became a huge bodybuilder. I was already big, and I drank the rest of the gallon." he started laughing in a manic way.
"I can hear that man laughing. Oh, no! Mom may have arrived, and he could be hitting her. Time to teach that jerk a lesson." he said, flexing and kissing his bowling ball biceps.
Kevin goes downstairs and sees the empty milk gallon. He hadn't think about it, but his dad laugh sounded deeper now, just like his own voice had become deeper after his growth spurt. And his groth spurt, the only thing he had was milk before the practice, and he admitted it had a funny taste. He had a bad feeling about it now.
Kevin goes to the basement, and he is shocked to see a huge giant sitting there. The coach barely fit in the basement now. He was five times a regular human, and the coach muscles were ten times the size of Kevin's. A huge pipe of hard meat was between his legs, the size of a really tall adult man. You could clearly see veins pumping power.
"Hello, son. Nice milk you bought... It definitely does a body good." the coach said, flexing his humongous biceps, the size of a Volkswagen beetle.
"What did you do?!"
"Oh, don't worry. You know how I always loved bodybuilding. I secretly wanted to be as huge as possible. And having a fatass son was a shame for me, but not anymore. We are the biggest alpha males on earth now."