That'll Buff

Meaning that everything will be ok in the end. Something bad has happened but it will work itself out in time. Nothing can harm you, you are invincible.

Guy 1: Damn I just wrecked my fucking car in a head on collision
Guy 2: That'll buff bro

Guy 1: Fuck. My gf just broke up with me, I'll be alone forever
Guy 2: That'll buff bro, you'll find someone