CJ's "Glasgow Grin" hides a shocking secret; it's not a scar at all. Those are his actual lips!
In this AU, the "couldn't stop smiling" bit in the story had nothing to do with actually smiling. His skull and facial structure were transforming grotesquely, as a result of the curse laserpotato.deviantart.com/art…
, and his jawline was altering. He appeared to cut his cheeks, but in actuality he was "freeing up" his new lips. Soon after they were cut, they quickly healed over. It was a natural part of the transformation process.
See? A scientific, plausible explanation of why CJ didn't die of infection/blood loss from cutting his mouth. Neener neener neener.
As you can see, CJ has far larger jaw muscles than a normal human's. This is what gives him his astounding bite strength.
Jeff the Killer (c) creepypasta
Cannibal Jeff (c)
CJ's bio: laserpotato.deviantart.com/art…