How much mechanical stress can a skeletal muscle bear?
The skeletal muscle is not isotropic and therefore the effect of stress would be different from different axes. The strength also depends on the density of fibers and the composition of tendons (aponeurosis) that connect the muscle tissues; these can change (positively) with long term exercise [ref].

In this article the authors show the effect of different mechanical stresses on the skeletal muscle tissue — digitorum longus, from rabbit hindlimbs.


  Tests were performed on extensor digitorum longus (EDL) muscles,
  chosen for its regular cross-section and low pennation angle (Lieber
  and Blevins, 1989). To ensure that only muscle tissue was tested,
  aponeuroses were carefully dissected away


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Figure from the same article by Morrow et al. (2010)

You can notice that the yielding point to longitudinal extension is somewhere near 180kPa. It can be assumed that a hook into the tissue on pulling would generate longitudinal extension stress (unless the hook pierces through the muscle tissue or has sharp edges that can rip the muscle transversely). The stress in the Bobby situation would be: $$\frac{\text{weight (mass)}\times \text{gravitational acceleration}\ (9.8\ ms^{-2})}{\text{area of the muscle covered by the hook} \times \text{number of hooks}}$$

This is the best I can answer your question based on data; this cannot be directly extrapolated to the Bobby situation because:


The muscle tissue is different
The strength of the tissue depends on how much has Bobby exercised his muscles. 
There would be additional mechanical stresses in other directions because of his movement while being suspended from the hook. 


Ribs are not very strong bones and attempt to hook something on it may cause punctured lungs, not pneumothorax. Death will depend on the severity of the wound.