Chip Kelly, the coach of the (American) football Philadelphia Eagles was questioned the other day about the Eagles’ play calling: specifically, why relatively few plays have been called for star running back DeMarco Murray to carry the ball. Kelly replied in part: “I would love to get everybody in a right lather and going, but when we’re not having success running the ball at all, then it’s tough to say, ‘Hey, we’re just going to make sure we get [running back DeMarco Murray] 22 carries and he’s lathered up.'”
OK, so the “lather” thing is taken from horse racing, referring to the frothy sweat of a horse. The OED cites an 1837 novel: “Miss Bell had already exercised her [a mare] so well, that, to use a jockey term, she was all in a lather.” The novel is British, but I sense that “in a lather” has been used in racing circles on both sides of the Atlantic.
You’ll notice that Kelly used the term, figuratively, in two different expressions. “In a lather” is a venerable one, but traditionally has been used to mean being in a state of high anxiety, irritation and/or agitation. The OED’s first citation is from Frances Trollope, quoting an American in 1849: “Don’t be in a lather, father, before you are shaved. I’ll do your job, I expect, if you won’t be in such a tarnation fuss.”
“Lathered up” seems to have departed from horse-racing parlance rather more recently. Searching Google News, I find Kelly is not the only American coach to lately use it about human athletes, especially football players (who are often described with words and expressions traditionally associated with animals). A Louisiana college football coach was quoted as saying about a receiver, “It’s hard to get into a rhythm until you get lathered up a little bit, it’s like a running back.” And the San Francisco 49ers coach said of an injured player, “he will be out there and going through that extended stretch that we do and try to get him into the team, get him warmed up and lathered up.”
But the real reason Kelly’s quotes spawned this post is the first two words in “a right lather.” The OED defines this “right” as “colloq. (chiefly Brit. and Irish English). As an intensifier (usu. in derogatory and ironical contexts): complete, absolute, total, utter.” It cites The Observer writing in 1974: “‘The Government did not know that there was no settlement in writing, and how could an order apply to something which did not exist,’ he said. ‘The Government made a right mess of it.’”
I would hazard to say that until Chip Kelly spoke, this usage of “a right” has never been uttered, non-ironically, by an American.
notoneoffbritishisms.com 
I’m not sure I agree with the OED (is that allowed?)! I think ‘a right [something]’ means ‘a veritable…’ or a ‘a real…’ something, not an absolute or total something. Take “He’s a right wally” as an example of a colloquial expression where the words veritable, real or proper could be substituted for ‘right’. (Not that I’ve ever heard anyway say ‘a veritable wally’.) It’s more a way of saying ‘he really is a wally’ than ‘he’s a total wally’.
To me (BrE) ‘lathered up ‘ and ‘in a lather’ are beasts of a different lather. ‘In a lather’, as you say, is horselike. ‘Lathered up’ means applied with soap.
You’ll know it’s a real Britishism when they qualify the qualifier … it’s a right royal mess.
I grew up in Baltimore County, MD. (1960s and 70s) People often said, “That was right good,” with no irony.
I feel like the difference between American and British uses is the absence/presence of the word “a.” Like in a Western, a cowboy would say, “That was right kind of you, ma’am.” But Oliver Hardy says “a fine mess,” not “a right mess.”
“Right” is used in the Atlantic provinces of Canada in the sense of “really”, “truly”, “veritably.”
“Right nice day!”
Of course, the language of the Atlantic provinces ie, the Maritimes plus Newfoundland, is a mix of Scots, Irish and west of England.
Off topic I suppose.. But last year my wife and I flew from Exeter UK to St John’s NL via Dublin. At Dublin airport there was an announcement over the PA system which was so broadly Irish we were unable to understand it. I asked a couple sitting next to me if they could explain what was said. They replied in a clearly recognizable Canadian accent that they didnt understand a word either but they were traveling with friends from Newfoundland who had no difficulty understanding the announcement! As far as South West of England and Newfoundland goes, my daughters, all born in Plymouth Devon, were immediately struck by similarities in language in Newfoundland that they did not hear anywhere else in England.
It happens in other places too: https://www.youtube.com/watch?v=fhOUbTfin3I
(From M. Hulot’s Holiday.)
There’s a BBC reporter from a part of Canada – I think Nova Scotia – where there is a distinct Irish influence in the local speech. People here often speculate about her accent and that she might be Irish but no one thinks of Canada.
That will be Lyse Doucet. She has part Irish ancestry but was born in New Brunswick. I have friends who do exactly as you say and assume she is Irish. Mr Hulot’s holiday is an excellent film! Demonstrating the point admirably!! Although we did manage to go to the RIGHT ramp first time in Dublin!
I think the best way to understand this is is to consider ‘right’ as being equivalent to ‘real’ or ‘really’. The German language uses the word ‘recht’ in exactly the same way – to mean right as in correct), right as in not left, and right as in real or really.