Antonyms for "hadst a fling at" could include phrases such as "took seriously," "invested time in," or "approached with determination." These antonyms convey a sense of commitment and dedication to the task at hand, as opposed to the more casual and perhaps impulsive connotations of "hadst a fling at." Other antonyms might include phrases such as "ignored," "dismissed," or "avoided altogether." These antonyms suggest a lack of interest or engagement with the task or activity in question. Whether focused and dedicated or disinterested and dismissive, the antonyms for "hadst a fling at" offer different perspectives on how we approach tasks and challenges in our lives.