In this case, it's very clear that once Mace shouted "he has s KNIFE" and ManOfLegendz happens to be there at the same time is very unfortunate. Mace clearly staged this and got ManOfLegendz killed for no reason.

Bluecrayons had every single reason to kill ManOfLegendz as I would do the same in that case.
A very unfortunate mistake that happened because someone tried to be funny, in any case, Mace should have been verbal warned to not do that again as it tends to cause trouble.

EDIT


Reading through this again and the imgurs,

Bluecrayons stated "Obviously from an outside perspective it would look like you stabbed him" Saying this and not actually seeing ManOfLegendz killing someone is killing on sus.