Edited to add this prequel — the most common use of the phrase does not include the French article. See the statistics from Google ngram, for example:
First, the New Oxford American Dictionary definition:
enfant terrible • noun (plural: enfants terribles)
a person whose unconventional or controversial behavior or ideas shock, embarrass, or annoy others.
From the Corpus of Contemporary American English, it has quite a few hits. These include works of fiction, magazines, and some academic writings; I don't believe it is restricted to the academic style. Examples include:
- This neglect comes from the " destructive cartoon " that greeted Ellis in the early years: his image as a frivolous enfant terrible whose clipped prose was fit only for the MTV generation
- His unflattering reputation is a hangover from the Young Tom Doak era when he was architecture's enfant terrible, better known for his Golf Magazine writings on the craft than for his practice of it.
- Krenek (1900-1991) was an enfant terrible among composers, but a series of artistic setbacks prompted him to reconsider his career. In 1925, he began work on…
- Eugeni Berzin, 25, the Russian enfant terrible who won the' 94 Giro and is scheduled to make his debut in the Tour
- It also reveals that, at 71, this seminal artist still is the enfant terrible he was when he began to rattle art's cages half a century ago.
- Make no mistake, the high points of this 96-year-old enfant terrible are remarkable.
To sum it up, I would say that most uses fall under two categories: (ⅰ) young professionals or artists who are seen as behaving unconventionally or in a shocking manner; (ⅱ) in an ironic fashion, for rather older people who behave in a way that is more expected of the young.
I found only one hit for the plural form which does not refer to Cocteau’s movie:
Yet he writes with a riotous, slangy precision reminiscent of a line of British enfants terribles, beginning with Evelyn Waugh in the 1920s-30s and continuing in such contemporary figures as Martin Amis and Will Self.