The worst performer on the benchmark index was Kentucky Fried Chicken merchant Collins Foods. It crashed 19.8 per cent after telling investors that wage increases and rising food input costs crunched its profit margins in the half year ended October 30. The owner of 264 KFC outlets in Australia saw some $200 million wiped from its market value as CEO Drew O’Malley said the group would lift menu prices in a measured way to avoid annoying customers and disrupting the value equation of the brand. “That whole [fast food] space is suffering from costs going up, and they’ve been reluctant…