Curate, connect, and discover
Jason obviously has things he's ashamed of, even though he's this ass-kicking God we all love, he still has his demons. One of those demons being certain scars. Ever Hero, vigilante, and Villain has those certain scars that they don't want people to see or know of. For Jason, it's the ones from the Laz pit and when he died. He hates them, wishes he could get rid of them, but they're a part of him.
Bart has scars of his own, one's he wishes to never show. That being, all of them. He shows people his outter shell, this fun, party loving speedster that's always quick with a joke. In reality he hides most his pain behind that mask because no one expects the outgoing one to be the most damaged, but that's just what he is. Damaged. So damaged he fears peoples reactions to his real self and became his character "impulse". The scars from the future, from being enslaved and tortured, from fighting back and losing so much. He hardly looks at himself because of them. He may be quick to heal but the scars run deep.
Jason and Bart find a mutual understanding in not wanting to share the scars stories and be complacent in showing them, but not showing off. It's better that way.