pack pusher
A pack pusher is someone who thinks they’re a superhero and starts running like they’re about to save the world, making the rest of the group feel like they’re the villain.
He ran like he was going to win a medal, and now I'm just trying to keep up and not fall over.
She started running like she was going to run the marathon by herself, and now I'm just trying not to cry.
He ran like a maniac, and I'm just trying to remember why I ever joined this group.