Pessimal

[Latin-based antonym for 'optimal']

adj. Maximally bad.

"This is a pessimal situation."

Also 'pessimize' vt. To make as bad as possible. These words are the obvious Latin-based antonyms for 'optimal' and 'optimize', but for some reason they do not appear in most English dictionaries, although 'pessimize' is listed in the OED.