The mentally ill can also be the guy who makes people feel uncomfortable, and is victim of an attack because of that. The difference between self defense and manslaughter against a mentally ill victim is whether what Neely said rises to the level that deadly force needs to be used against him.
Luckily, all witnesses agree on what he said. Unfortunately, what he said was not a clearly thought out thing.
The difference is whether a reasonable person would know if they are a danger to others. "Uncomfortable" was not what was going on here, the man threatened folks.