Im interested in using different applications of aim constraints and or OrientConstraints and the difference. You flirted about doing a tutorial last year on twitter. With your schedule being packed I understand. One application would be blowie. I know what I want to achieve but not knowing which bones to use. Also, how would you removed the constraint if I make a mistake. Cheers, Thanks again for your Hard work.
So the nice thing about constraints (and this isn't at all intuitive or explained anywhere within SFM's official documentation) is that they're actually sliders. If you select the constraint in the Animation Set Editor, you can adjust its value between 0 and 1 like you would a flex slider. A value of 1 (default) means the constraint is fully in control and you can't pose the constrained bones (moving, rotating, or both; depending on the constraint in question). A value of 0 means the constraint is fully disabled, meaning you can pose it as if the constraint were never there. Values in-between are weird combinations of the two.
What I would personally do is apply aim-constraints on both the head and the neck bones of the giver, and actually have them target a dummy bone, rather than any actual bone on the receiver. I use the axis_helper.mdl model as my dummy. I would lock and zero the dummy to the base of the receiver's cock, aim-constrain the giver's neck and head bones to that dummy, and then set the values of the constraints to something like maybe 90% on the head (so you can tweak it if you have to), and 50% on the neck.
Then you let the aim constrain do the bulk of the work, while still being able to move the dummy around if it starts getting funky, and even manually tweaking the neck/head bones if you have to.
Constraints are very interesting and open the doors to very creative applications! I definitely recommend experimenting with them!