The terms: <em>anti -</em><em> </em>or <em>syn-</em><em> </em> as an addition to a word, when they occur, are "prefixes" that occur at the beginning of the word. These prefixes means "without" ; "against" ; or "lacking" .
I would say he would use words that make his tone sound sarcastic in the readers mind. Or after the character's line it would say...EXAMPLE: "Oh really" Alice said sarcastically