The phrase "most belly-aching" is used to describe someone who complains excessively and constantly. Some synonyms for this phrase could include the following: whiniest, most grumbling, most griping, most moaning, most groaning, most carping, most kvetching, most grouching, most bellyaching, and most murmuring. All of these words describe someone who is complaining incessantly about something and can be used interchangeably with "most belly-aching." It's important to note that constantly complaining can be irritating and negative, and it's essential to focus on finding solutions and positivity instead of constantly complaining.