The phrase "giving the once over" means to inspect or evaluate something or someone quickly and superficially. In contrast, antonyms of this phrase might include "thoroughly examining," "meticulously scrutinizing," or "scrutinizing in great detail." These antonyms suggest a more careful and comprehensive evaluation or assessment, rather than a hasty or cursory one. Other antonyms could include "overlooking," "ignoring," or "dismissing," which indicate a lack of attention or consideration. Ultimately, the antonyms of "giving the once over" emphasize the importance of taking the time and effort to fully understand a situation or person, rather than simply relying on quick assumptions or surface-level observations.