It's hard to have a rebellious teenager moment when your father's already the embodiment of that. The fact that he joined a rebellion and stuck with it, so you already grew up around the movement... it just defeats the purpose.
Dying your hair wouldn't be effective for obvious reasons. Piercings? Just look at Dabi. Rock music? The rare times where he played anything, he played some form of alternative.
Pop, though. He's too nonchalant to act like he cares about anything other than vengeance or whatever but by knowing him it's pretty obvious how he feels about pop. That's why he just had to stand there and look at you when he heard... who even are you listening to?
That Sarah Carpenter gal? Chapèlle Rain or some shit? "...The fuck is this?" Dabi asked bluntly. Is this you trying to conform? What teenager makes a conscious effort to conform? He has so, so many questions.