Currently OnParticleCollision will trigger when hit with any particle or if the particle hits anything. Getting around these issues requires really annoying work-arounds with layer settings and sub-emitters.

It would be a lot better if you could specify what layers trigger OnParticleCollision in the same way as OnEnter/Exit Trigger/Collider.

Specifically, this would allow for pretty consistent hit detection for particle guns, and could also prevent people from being able to use their avatar particles in certain PvE worlds (if the world creator wanted it that way, of course).