If you haven't heard the song, please go listen to it once. I'll wait. Here's a link to the music video:
https://www.youtube.com/watch?v=UprcpdwuwCg&noredirect=1
...........................................................................................................You're back? Great!
In my opinion, the song is about the church. The chorus says "All my friends are Heathens" In the church HEATHENS is a more degrading word for sinners, or people with an ungodly lifestyle. The rest of the chorus warns against making hasty judgments against the HEATHENS. This just feels like it relates to the church more than Twenty-One Pilots fans, depressed kids, or even the Suicide Squad from DC.
The bridge (I guess it's the bridge. I don't know a lot about music so correct me if I'm wrong) is "You will never know the murderer sitting next to you. You will never know the psychopath sitting next to you. You will think how'd I get here sitting next to you..." The use of the words murderer and psychopath actually do make me think SUICIDE SQUAD, but if we stick with the church interpretation, the lyrics still fit. Christians tend to be quick to judge one sin as bigger than another (actually all people do this, but it's more obvious when a Christian does it). We never know what the person next to us is really going through.
Hope you enjoy re-listening to this song with my interpretation in mind!