A substitute word dat you use to diplomatically avoid having to come right out and say dat someone is nutso.
Phrases like, "He's seeing someone about that" or "He's on medication" could loosely be termed as "synonimh sayings" for more-humiliating word-choices to mean dat da person under discussion isn't playing wif a full deck.
A creatively-alternative word-choice for more-diplomatically opining dat someoneneeds to check himself into da loony bin.
Seinfeld and his buddies spent an entire half-hour show merely trying to avoid determining whether Lloyd Braun is still crazy, when they could just have used a synonihm or two and thus probably saved Lloyd's feelings.