Garry's Mod Wiki

Entity:CollisionRulesChanged

  Entity:CollisionRulesChanged()

Description

Declares that the collision rules of the entity have changed, and subsequent calls for GM:ShouldCollide with this entity may return a different value than they did previously.

This function must not be called inside of GM:ShouldCollide. Instead, it must be called in advance when the condition is known to change.
Failure to use this function correctly will result in a crash of the physics engine.