Role of Mutations

Some sexual ornamentations would probably qualify as counter-functional. It doesn't seem very functional to carry around a (literal) assload of feathers twenty times the size of your body, or be nice and brightly colored to stand out to predators as well as potential mates. Not sure if these qualify as "counter-functional", but they don't seem to be very "practical" except for sexiness purposes...

I know what your getting at, and I'm trying to think of an example...But animal "function" is a bit vague, too. It seems to me that there are many species with female mate choice where the males have given up the "function" of camoflaging pigmentation patterns in favor of insanely bright colors. (The females by comparison are drab, retaining the camoflage "function" that the males have lost).