It’s a nice shirt. I do share the sentiment but I’m not sure the phrase “grow up” is correct (ever notice utterances like “oh, grow up” and “real mature! /s” are made disproportionately by preteens…just something to ponder). If the meaning is refusing to conform to societal norms then I wholeheartedly agree! 
I’m not liking how knowledge by consensus, and that being motivated mostly by fear, has been becoming our societal norm for quite some time now (despite warnings from Huxley, but hey,who has time to read books now…gah :() That may actually be the core issue (?).
Our society now demands adamant opinions immediately and many do not have the time to think about positions before adopting them. For example, did anyone consider that google uses a technology called content ID to vet the videos they host on youtube (and in some cases even pay the appropriate royalties if necessary) or that this site is protected by safe harbour laws (known as frameworks internationally) should any of us forum users actually do anything wrong?
Nobody is doing anything wrong from an ethical or legal perspective by sharing content from youtube here. Any content. In fact, personally, as a Canadian I’ve benefited greatly from people sharing their UK and European cultures on these forums. That’s not wrong and that should be encouraged. Especially derivative works; Some of the best pieces are just that. For example I wish someone would make a death metal cover (I’m talentless and can’t :() of The Rainbow Connection because that’s exactly what plays in my mind whenever I see a thread like this one.