On the definition of his name, Gumba challenged his chicken shit enemies and creed-hating imitators to grow some and stop being so scared of tackling him in a real flame war.
You're sitting at a stop sign hoping to make a left, and the person in front of you is also attempting to make a left turn. However, this person in front of you is being very timid about reading traffic and making his move and you're increasingly pissed because he's missing oppertunities so you start screaming "Grow Some!"
A boy that acts as if he doesn’t know you, even though you know he does, and is being rude about it. You end up thinking that maybe he hasn’t grown his balls yet.