When you put on your dad's old trainers, which he wore years ago when he lifted more heavily than now, you start to feel strange again. The arms of your polo shirt start to constrict more as the muscles start to bulge further and further out. The seams start to fray as your arms inflate, slowly but surely gaining mass. You look down as the your chest is following suit. At the same time, the beer belly is slowly deflating, but it's hard to see over your ever expanding chest.
At the same time, your scalp itches as hair starts to return back slightly. You're definitely still balder than before, but it's less prominent now.
In a few minutes, you've remade yourself into a 30-something giant of a man. You still look like you as the transformation did not turn you again into a clone of your father at that age, but you've somehow gained his body attributes of that time. The surge in size is intoxicating. You can't help but head over into your parents' bathroom and stroke yourself until you climax. Your body starts to feel more your own. You stare back at the reflection in the mirror of this football player sized man and the reflection doesn't feel as alien as it did before. For a moment, your memories of being the scrawny teen start to fade, but they're interrupted as you hear John, you mean your father, calling for you to hurry up so that you can escape before your wife, er, mother returns home.
After cleaning yourself up a bit, you head back toward the entranceway where your father is waiting. He's put on your old clothes and stares in awe at you as once again you've changed your appearance.
"What did you do this time?" he demands.
"I put on your old trainers that you haven't worn in ages, somehow I gained your old physique." you state proudly, flexing your arms a bit. You hear a slight rip as the sleeves start to give way a tiny bit. The muscles are proportionally bigger to your slightly taller frame, so your father's shirt is slightly smaller on you than it would have been for your father at that age.
"Wait, if you changed, why did I not change too!?" he exclaims with frustration. Apparently, the novelty of gaining a teenage body again was starting to wear thin, especially in light of his son's increasingly intimidating transformations.
You can't help yourself as you go toward your father and pick him up under his arms, putting you face to face with him, his legs suspended in air. The feeling of power overwhelms you, but for only a split second as you see your father's terror. It grips you like a cold hand causing you to put him back down again plaintively.
"We should find that shop," you state in your deep, rich baritone. You don't want to give up your body as it is, but you can't stay in it. How could the world understand everything that's happened to you and your father? Boys don't just turn into men and vice-versa. Your life as it was would be over and you and your father would be adrift.
"Let's go, Dad," your father blurts, then catches himself. You look in horror at him as you realize that his new identity is starting to settle into him as it did you temporarily. Could it be that the socks are not just changing your bodies, but also changing your minds as well? Quickly, you grab his wallet and notice that the driver's license photo has changed somewhat. The picture in there had changed somewhat. It's no longer the face that your father had as you start to notice the sandier hair. The photo in the license was starting to match your face as it is now. It's not just you, but reality that's also changing, and if you did not do something soon, you and your father will lose what you were before the socks.