Most rejuvenating means something that revives, refreshes and reenergizes you. Therefore, the antonyms or words opposite in meaning to this phrase, would be something that exhausts, drains, stresses or fatigues you. Some examples of antonyms for most rejuvenating are wearisome, tiring, draining, sapping, and enervating. If something is wearisome, it is causing fatigue or boredom. If something is tiring, it is tedious and exhausting. If something is sapping, it is causing you to lose energy and enthusiasm. If something is enervating, it is making you feel drained and weakened. Overall, the antonyms of most rejuvenating are anything that lacks vitality or drains your energy, leaving you feeling tired and disheartened.