The phrase "fly in the face of" means to go against or contradict something. It is a strong expression that implies defiance or opposition. Some synonyms for this phrase include "defy," "challenge," "oppose," "contradict," "disobey," "disregard," "go against," "violate," and "flout." Each of these words carries a similar meaning and can be used interchangeably with "fly in the face of." Whether you are writing a formal paper, a news article, or a casual blog post, choosing one of these synonyms to replace "fly in the face of" can help add variety to your writing and make your message more impactful.