Antonyms for the phrase "piece of pie" include challenging, difficult, daunting, hard, complicated, intricate, and complex. These words describe situations or tasks that are not easy to accomplish and require more effort and skill than a simple and straightforward task like cutting and eating a slice of pie. Antonyms for "piece of pie" may also indicate a lack of simplicity or predictability, such as uncertain, unpredictable, risky, or hazardous. In general, antonyms for "piece of pie" refer to anything that is arduous, demanding, formidable, or risky compared to the simple pleasure of enjoying a delicious slice of pie.