This is Super Mario Randomness 3 - LuigiFan's Voice Revealed.
Super Mario Randomness 3 Luigifan's Voice Revealed!
This is the video.
Events
Starman3 starts talking to LuigiFan54321, who reveals his voice to sound like a kid. Super and Captain are both surprised, as is Starman, who all question why he sounds like a kid if he has things like the Elemental Stars and such a good drawing skill. Super wonders when he'll hit puberty as LuigiFan is annoyed, as Starman judges. LuigiFan gets annoyed and demands an apology after Captain walks off not wanting to be involved. Super apologises, as Starman tries, but fails, and gets owned. Supersonic puts some text in the moral, as he gets owned in the end as well.