This is a scarf in the wind for Rexouium.
To get the intended effect, add Dynamic Bone to Bone.002 and Bone.011
How to install:
Import the package.
Move the Prefab to your Avatar Root and position it so that it fits the neck.
Unpack the Prefab and move each bone under Armature to the corresponding bone in your Avatar's Armature. So that Neck goes under Neck, Head goes under Head and so on.
Suggested Dynamic Bone Settings:
Colliders: Neck (DynamicBoneCollider)