The phrase "rain on" typically means to spoil or ruin something. To express the same sentiment, some synonyms of this phrase include "put a damper on," "ruin," "spoil," "ruin the parade," "ruin the fun," "spoil the mood," "dampen the spirit," "cast a shadow on," "ruin the moment," "spoil the occasion," and "ruin the day." These synonyms are commonly used in casual conversations, writing, and public speaking. One can replace the phrase "rain on" with any of these synonyms based on the situation to provide a better understanding of the intended meaning.