"Going daffy" is an informal expression that means becoming crazy, irrational, or losing one's mind. There are several other synonyms for this term that can be used to describe this condition. Some of the common synonyms for "going daffy" are going insane, going nuts, losing it, cracking up, becoming unhinged, and tipping over the edge. These terms can be used interchangeably depending on the context and the severity of the situation. It is important to note that these expressions are colloquial and should be used with caution in formal settings. It is crucial to be mindful of the audience and context while using such expressions.