OHHH BABY A TRIPLE
Requires VRCFury
Drag the Boop Hitmarker prefab onto the root of your avatar (the main one with your VRCAvatarDescriptor), so that it is a child object of the root object (not of any armature bone)
In the 3D view, position the Boop Hitmarker object within your character's nose, and adjust the radius of the VRC Contact Receiver
Upload your avatar, and VRCFury will build it into your avatar.
Hitmarker is enabled by default, and you can toggle it in your in-game radial menu.