Most popular in games like Halo or CoD, noobtubbing is the act of overly using of the Brute Shot or Barrel-mounted grenade launcher, respectively.
Doing this, more often than not, makes other players dislike you, avoid you, or call you a noob.
a nuke: Dude, the only wep he uses is the brute shot.
A Prinny Dood: Forget him. He's just noobtubbing. Let's join another server.