Antagonyms are single words that have meanings that contradict each other.

A current example would be "BAD". There is the normal meaning and the slang meaning of "good" (sometimes pronounced baad for emphasis). Although words in which the antithetical definitions are listed in common dictionaries are preferable, well-known slang examples are also acceptable.

Antagonistic phrases, usually informal -- These are phrases that (probably through corruption) have come to mean the opposite of what they should mean if taken literally. Pairs of phrases, usually informal, -- how can they mean the same? Confusing words (should we call them "confusonyms"?) To have or to have not -- These terms are confusing and have opposite meanings depending on usage.