Peyronie's disease is a rare condition involving a deposit of scar tissue or plaque in the erectile tissue in the penis, sometimes causing painful and curved erections. A fellow nicknamed Berg suffered from a severe case of Peyronie's disease. As a result, his erect penis had a significant curvature. This gave rise to the somewhat popular saying "bent like a Berg cock".
A football player breaks his ankle out on the field, so he tells the physio "man my ankle's Bent like a Berg cock ".