There are several different synonyms that can be used for the phrase "was irresponsible". Some examples include reckless, careless, thoughtless, inconsiderate, and negligent. These words all carry slightly different connotations, but they all suggest that the person in question was not being responsible or attentive to their duties or obligations. Whether it's a failure to consider the potential risks of a particular course of action, a disregard for the safety or well-being of others, or simply a lack of mindfulness or attention to detail, being irresponsible can have serious consequences. By using precise and evocative language to describe irresponsible behavior, we can better understand and address the underlying issues.