I was recently talking with a professor at an American university who regularly brought students to London for study-abroad programs. (He’s now retired.) He said that by the end of the semester, his male students had always incorporated into their vocabulary three insults: wanker, tosser, and poser. I’ve covered the first here (and touched on it several other times: plug it into the “Search” field at right to see). As for “tosser,” the OED defines it as “A term of contempt or abuse for a person; a ‘jerk,'” and etymologically originates it in the same activity as “wanker.” But it seems to be used rarely if at all in the U.S.
However, “poser” is worth looking into. Here’s what the OED has to say:
Since “poseur,” from the French, is an almost identically-spelled synonym, it’s worth looking at the OED deets:
This suggests to me that “poseur” has been out and about since circa 1870; the Time and Maxim (American lad magazine) citations and a Google Ngram Viewer chart suggest it’s been used with relatively equal frequency in the U.S. and Britain.
The Anglicized “poser” is trickier. First, note all the citations are British. Second, I suggest that the Pall Mall Gazette and Shaw (” The man..is young, agile, a talker, a poser, sharp enough to be capable of anything except honesty or altruistic considerations of any kind”) quotes are interesting outliers, in which the straightforward noun “poser,” one who poses, is extended to the derogatory meaning the word would later come to adopt. Even the 1987 Guardian quote (“I’ve always been a poser,..but the first time I did a modelling job I was shit scared”) seems to refer to literal posing. Only the final quote, from The Sun, sounds like the “poser” one is used to today: “The former World Cup striker is shown as a precious poser who wears a blond wig and refuses to play if it’s raining.”
It’s a little hard to be definitive with “poser,” since in database searches I’ve found it impossible to separate out two other meanings of the word: a hard-to-answer question (“that’s a real poser”) and a French verb meaning to put or to place. But assuming that “poser”=”poseur” had taken hold in the 1980s (by which time “poser”=tough question had fallen out of fashion), Ngram Viewer shows almost twice as frequent use in U.K. as in U.S. (As I’m fond of saying, reliable data for Ngram Viewer only goes up to 2000.)
But the word has caught on on this side of the pond. The main character in a new Broadway play by Tracey Letts says Radiohead’s Thom Yorke is nothing but a “scrubby little poser.” (I know Yorke is English, but Letts is a Yank.) The headline of an ad in the New York Times reads
Getting Digital Right: Posers, Players and Profits
And last month Forbes had:
Peak Performer Vs. Professional Poser: Creating The Right Team
Earlier this year, Times columnist Maureen Dowd wrote that Democratic presidential candidate Beto O’Rourke has been compared to “a middle-school poser who ‘went to Zumiez and spent $27 on stickers.'”
Don’t ask me to explain that. I only come up with the quotes, not what they mean.
notoneoffbritishisms.com 
I think the last time I called or referred to someone a ‘poser’ or ‘such a poser’ was when I was at school.
Thanks. A new bookmark to help me explain British English to my students.
I second what Anthony said. ‘Poser’ was definitely common growing up in the Boston area (MA, USA) but mostly fell outta the lexicon after a certain age.
I picked up poser, tosser and wanker reading the British music press, (NME, Sounds, etc) in the mid to late 1970s. A lot of people I knew then did too.
I distinctly remember worrying about the pronunciation of ‘poseur’ back in 1976, the heyday of the London Punk scene. Poseurs were often derided. They were those who just came to stare, gaining a little street cred by wearing fake safety pins and bin bags, but afraid to embrace full anarcho-spittiness. But was ‘poseur’ pronounced with a French accent? I didn’t know and therefore avoided using it. This goes to show that although it was in common use with that spelling – and I’d read the word in the music press and fanzines – I’d not actually heard it. It was just pronounced ‘poser’, by the way!
As I think I remember it, if one wanted to add an extra slice of mockery, one would pronounce it with the French ending.
I wnder if poser is more a working and middle class insult and the French flaneur apply to the male upper class equivalent? I doubt that flaneur would cross the Atlantic though.
Nice to see the spike for “poser” in the UK during the New Romantic pop era. Starting, I think, with Adam Ant and running though until Duran Duran fell apart.
Adam Ant’s Prince Charming has the “reclaimed” meaning used for poser here:
Prince Charming **ridicule is nothing to be scared** of /don’t you ever, don’t you ever stop being dandy, showing me you’re handsome.
For more https://en.wikipedia.org/wiki/Blitz_Kids
I first came across the word in 1976 during the era of the King’s Road punks. It was equally applied to the Sloanes in the area too.
“Poser” is just an alternate spelling of “poseur”. The only difference is that if you spell it poser, you’re suggesting to the reader not to pronounce it in a Frenchified manner, which would remain an option if spelled “poseur”.