Well there's a ton of them but I'll list off some of my favorites

Kirk Cameron's crop top when he started acting, didn't know how much of a effect this would have on boyactors after him
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Christian Bale saying he wanted to be a hedgehog when he was 5 in his Terry Wogan interview
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The shower scene in Lucas where the bullis accuse him of being gay
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Devon Sawa in Casper (ton of 90s kids loved it)
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Ricky Schroeder winning a golden globe and being the youngest actor to win one at the age of 9 for his role in the Champ, I was going to put that one scene in the champ but I didn't want to spoil it
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Edward Furlongs American flag shirt he wore at the premiere of American Heart
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Gary Colemans Iconic "Whatcha talkin bout Willis" in Different Strokes
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Rusty's beer scene in National Lampoons Vacation
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Ilan Mitchell Smith's wearing lady's underwear in Weird Science
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When Boyactor Enthusiastic in the 80s mistakenly labeled Matthew Broderick and Michael J Fox as Boyactors because they looked young but were actually in their early 20s, they never bothered to fix it which lead to MB & MJF to be known as the oldest boyactors
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The gay moments in The Devil's Playground wow that movie will never be handled well today
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The entirety Of Groovy Greg in The Brady Bunch, every moment with Greg was a beautiful one
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Ryan Goslings 1992 CTV interview where he just makes funny faces for the entire time, you can tell he didn't want to be there
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Along the same lines as Jetboy:
In 'We Kids of Bahnhof Zoo', homeless Detlev and his girlfriend Christiane F. are crashing on a sofa at the apartment of Detlev's sugar daddy.  In the middle of the night, Christiane is woken by the sound of Detlev 'paying rent' behind the bedroom door.  Christiane covers her ears to block out Detlev's noize, while I nearly fainted in the theater from my pounding heart.  The sound off-camera was more distressing than any image could be.
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Christiane can't stand it anymore and opens the bedroom door to catch Detlev with his sugar daddy.  "What else can I do?" cries the helpless Detlev.

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