Achille12345's entire videography from (arguably) The Random Game onwards is a long string of these moments. Standout examples are SuperGunfight and The Secret Game.
Skies of CD-I Legends. The King and Link as Back-to-Back Badasses, clearing out entire roomfuls of mooks by themselves, Mario and Luigi beating the crap out of Iron Knuckles using the Enclosed Instruction Booklet, Sky battles rivalling Super Mario Bros. Z in destruction...
In The Fat Controller Doesn't Need his Jacket, the titular character, interrupted from his regular viewing of Chobits, violently beheads the postmanDemoman- voiced terrorist Tom Tipper with a katana.
The IM Gay trilogy by kwarkman85. Not only do you have IM Meen take several levels in badass by defeating Hectan and then snidely rejecting Ganon's offer to join him and then trapping him in the book of Koridai, you have Link changing from a naive ditz to a certified Badass after Meen also traps Zelda and The King in the book of Koridai. And then there's the showdown between the two in the conclusion of the trilogy.
Just the fact that YouTube Poop has been so well received, it resulted in about 250 YouTube Poops coming out on DVD & Blu-Ray! Their title is called "They Pinch Back: The Best of YouTube Poop".
