"Be caught with your pants down" is an idiom that means being caught in an embarrassing or compromising situation. Some synonyms for this phrase are "be caught off guard", "be caught unprepared", "be taken by surprise", "be caught in the act", "be in a sticky situation", "be in a tight spot", "be in a pinch", "be in a dilemma", "be in trouble", "be in a fix", and "be in a predicament". These phrases can be used interchangeably with "be caught with your pants down" depending on the context of the situation.