How they meet.
Sam and Dean are just fighting ghosts and demons (like they usually do) and the Flash accidentally runs in on them because he was told that there were people in trouble. Sam's like "get out here it's not safe" and Dean pulls this face (one of peer surprise) and is like "dude do you know this is?!... It's the Flash!", And Cas comes in from somewhere (like he always does) and is like, "we seem to have come upon a meta-human based world" in that same loveable voice, and Dean's like "no shit Cas, you think". And Sam's off to side like "guys this is no time have one of your relationship fight".
