When the cast of 'It's Always Sunny in Philadelphia' cast showed up at Comic-Con dressed as the characters from the show's epic, ridiculous rock opera episode "The Nightman Cometh," it was pretty inevitable that they would end up doing a musical number.

So here they are, pleasing the crowd with a sing-a-long rendition of 'Day Man,' from that episode.

Watch the original version of the song from the show: