The phrase "as a fruitcake" is correct and usable in written English.
It can be used to describe someone as eccentric or crazy, often in a humorous or light-hearted context.
Example: "After hearing his wild conspiracy theories, I couldn't help but think he was acting as a fruitcake."
Alternatives: "as crazy as a loon" or "as nutty as a fruitcake."
"I've been saying that for years and have been regarded as a fruitcake.
"The feeling is, 'Well, we're not nutty as a fruitcake, so it couldn't have done us much harm,"' he said.
[Yiddish: bonkers, off his squash, nutty as a fruitcake, a cuckoo bird.] Could this actually be Sigmund Freud's diagnosis of Carl Jung?
Then, Eugene O'Neill, in his 1914 play, "The Movie Man," coined a memorable simile: "We sure are as nutty as a fruitcake or we wouldn't be here".
Every holiday season, either out of respect for tradition or sheer spite, at least one Hollywood studio is sure to release a drippily sentimental, gratingly cheerful "comedy," indigestible as a fruitcake and disposable as wrapping paper.
I covered the shows for this paper for eight years, and while it is extremely easy to defend fashion itself on a feminist level, the fashion industry, and in particular the fashion weeks, are about as feminist as a fruitcake.
Mackey, for years a media and stock-market sweetheart, was suddenly recast as a monopolist, a fruitcake, and a sneak.
But could he embrace the party of Ross Perot, the man Senator McCain once described as "nuttier than a fruitcake"?
Moroccan attacker Adel Taarabt was a player Redknapp famously described as "a bit of a fruitcake" after selling him to QPR for £1m when he was in charge at Spurs.
The film opens by crisply demolishing L Ron Hubbard as a charismatic fruitcake rather than the war hero of his official biography.
And yes, career-wise, I didn't want to be branded as a big fruitcake and that's all I could do.
