How to make a rigid body pass through only certain other rigid bodies? I have a human model made of separate objects. Body, thighs, legs, feet, toes, etc. I got the body to collide with the toes and not pass through each other. However, I want the thigh and leg capsules to be placed so their ends overlap, and are able to rotate, as if they can pass through each other. But they must not pass through say the toes when they collide. I thought about Groups but no progress. The human will be able to feel around its body, so, setting limits won't stop it from "puncturing" itself with its finger at any area. Therefore a all-can-pass-each-other solution won't work. The calves behind the knees would, if both can pass each other like want, would actually need set limit rotations, but that works there.
Rigid bodies collisions do not allow the kind of control you describe so, instead, a different approach is required.

First model the system using non-overlapping rigid bodies - create the rigid bodies and enable collision and use Rigid Body Constraints to set up the relationships between them.



The constraints can be easily created using the 'Connect' button in the Physics tab of the 3d view Tool Shelf (T). However, for each connection you need to uncheck the Disable Collisions property in the Rigid Body Constraints panel so that the collisions remain active.




To add the overlapping elements, create new objects and size and position them as desired and parent each one to the relevant rigid body (select the new object, hold Shift and select the associated rigid body, then press Ctrl+P and select 'Object') - they will now follow the motion of the associated rigid body.

Since the overlapping elements are no longer rigid bodies they do not affect the collision (and so can overlap) while the (non-overlapping) rigid bodies can handle the physics. You can 'hide' the rigid body 'skeleton' by moving it to another layer if desired - or simply set it not to render (click the camera icon against each object in the Outliner).



To take this a step further you could parent bones to the rigid bodies and have those deform a mesh that would act as a 'skin' to the rigid body skeleton. This is more complicated but would produce much more convincing joint motion for 'organic' characters.