The term "acme of frivolity" refers to the peak or epitome of a superficial or meaningless act or behavior. Some synonyms for this phrase could include the "height of triviality," the "apex of triviality," the "zenith of superficiality," or the "pinnacle of empty amusement." Each of these phrases highlights the idea that the behavior in question has no substantial value or purpose. Other potential synonyms could include "ultimate flightiness," "unrivaled triviality," or "supreme frivolity." The use of any of these phrases emphasizes the idea that the subject in question lacks any significant importance or substance.