There can be different definitions.

1. A grenade launcher or rifle grenade, in which makes people more pissy with extra explosives.
2. A general insult, used to make one feel special and good about themselves over a video game, specifically and more commonly in Call of Duty games.
3. Another way to accuse someone of being a fag or not being good at video games compared to the accuser.
4. A term that when used may cause the accused to become defensive, therefore declaring an intense 1 versus 1 private match battle to prove that they are better.
1"hey guys, I'm getting easy kills with the n00btube.

2. Matured Teenager "Hey kid, you are such a homo"

Annoying child " Fuck off dude, I'm b345T with the sniper, and you are just n00btubing"

Annoying child "*loudsmacking around in the backround* OH BABY, I AM TOO GOOD AT CALL OF DUTY"
3. "Hey, I saw you n00btubing with another guy behind the dumbster you n00b
4. MLG gangsta "I bet you n00btube all damn day!"

Clan member "You wanna bet bitch? Back out and I'll beat you 1v1.
by luap eoj April 26, 2010
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Someone who repetitively uploads stupid videos to the Internet. Specifically YouTube.
"Dude, check out my new video on YouTube!"
"That video is so stupid, you're such a n00btube."
by Kal-EL777 May 12, 2008
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