I can try :)
What should it do? Should players be able to just type !block, and for x seconds they can go through players?
EDIT: API has the flags, Here you go. Flag one (In value starting from 0, not NONE) should be your best bet for limited time.
COLLISION_GROUP_NONE = 0,
COLLISION_GROUP_DEBRIS, // Collides with nothing but world and static stuff
COLLISION_GROUP_DEBRIS_TRIGGER, // Same as debris, but hits triggers
COLLISION_GROUP_INTERACTIVE_DEBRIS, // Collides with everything except other interactive debris or debris
COLLISION_GROUP_INTERACTIVE, // Collides with everything except interactive debris or debris
COLLISION_GROUP_PLAYER,
COLLISION_GROUP_BREAKABLE_GLASS,
COLLISION_GROUP_VEHICLE,
COLLISION_GROUP_PLAYER_MOVEMENT, // For HL2, same as Collision_Group_Player
COLLISION_GROUP_NPC, // Generic NPC group
COLLISION_GROUP_IN_VEHICLE, // for any entity inside a vehicle
COLLISION_GROUP_WEAPON, // for any weapons that need collision detection
COLLISION_GROUP_VEHICLE_CLIP, // vehicle clip brush to restrict vehicle movement
COLLISION_GROUP_PROJECTILE, // Projectiles!
COLLISION_GROUP_DOOR_BLOCKER, // Blocks entities not permitted to get near moving doors
COLLISION_GROUP_PASSABLE_DOOR, // Doors that the player shouldn't collide with
COLLISION_GROUP_DISSOLVING, // Things that are dissolving are in this group
COLLISION_GROUP_PUSHAWAY, // Nonsolid on client and server, pushaway in player code
COLLISION_GROUP_NPC_ACTOR, // Used so NPCs in scripts ignore the player.