Over dinner in London, a fascinating discussion is launched by my American friend John A., who has been in-country for months but is struggling still with the local patois. How exactly should you use “brilliant”? The Brits around the table weigh in, but quickly grasp that it’s a tougher question than it looks.
Rule #1 is clear enough: grasp (as you easily might not) that its main use is not for strong emphasis but for the mildest of affirmations in ordinary situations:
Did you remember the milk? Yes. Brilliant.
I thank I’m finally getting over that cold. Brilliant.
But the compassionate-sarcastic-deflationary usage is rarely far away:
Who was that? My fifth spam call today. Brilliant. (“Tell me about it. Who are these bastards anyway?”)
And then there’s non-compassionate sarcasm:
Actually I quite enjoy doing my taxes. Brilliant. (“You’re a weirdo and I’m not sure I want to know about it.”)
Rule #2 might be: don’t use it to describe anyone or anything as actually, you know, brilliant. Or rather, understand that the “brilliant” in “Her research is in quantum cosmology; she’s brilliant” might as well be a completely different adjective.
Thus Rule #3: You can use “brilliant” (in the sense that worries John) only to show your assessment of a fact, an idea, an achievement, etc., not a person.
Another rule is: don’t say “dead brilliant” unless you’re Scottish. And note that “dead brilliant” really does, unlike the English (and Scottish) “brilliant,” indicate at least a degree of affirmation of genuine brilliance …
Scottish MP Mhairi Black’s speech against nuclear rearmament was dead brilliant.**
… though it can also be used sarcastically:
Apparently Trump is threatening to invade the Moon. Dead brilliant.
So, I said to John, you’re probably just going to carry on getting it wrong.
He rolled his eyes and said, quite correctly, “Brilliant.”
** [Indeed it was. And tragically she is right, both morally and militarily right, and those who control the purse-strings are tragically wrong, their judgement hijacked by their desperate neediness for shallow national prestige at any cost: https://www.youtube.com/watch?v=thVc6U25gOI.%5D