I'm gonna do it.
When someone says 'I'm gonna do it,' they're basically saying they're going to be the dumbest person in the room. It's like they're volunteering to get hurt just for fun.
I'm gonna do it. I'm gonna try to ride a bike with no hands.
I'm gonna do it. I'm gonna eat that whole cake even though it's 2 a. m.
I'm gonna do it. I'm gonna challenge him to a duel with toothpicks.