Not a Grockle! βρωμοτουρίστες!

Not a word listed by William Barnes in "A Glossary of the Dorset Dialect" (1886) either.

An invented word (according to Oxford English Dictionaries, and only dating back to the 1960s), much used by the author John Fowles, who lived in Lyme Regis. He couldn't trace the etymology of the word, which is a derogatory term for summer visitors or seaside holidaymakers in the West Country. "An annual nightmare", says Fowles. The word was possibly first heard (in the media) in the film "The System" (1964).

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"There are just too many of us these days. We have a dialect expression here in the west of England: “the grockles.” A “grockle” is someone ugly, but necessary: a visitor, a tourist, a foreigner. It is not just here in Dorset, but all over the world: the grockles begin to ruin everything.
 Places touch me, move me, far more. If I am lucky, now, in the present, visiting; but these days it seems more and more in memory they move me, what they were like. There is a beach on Spetsai in Greece I describe in The Magus. Later visitors have told me how the grockles have completely spoilt it. But I can still remember it as it once was". John Fowles, from Paris Review interview

He uses the word "grockles" in The Magus (1966): "Greece--why hadn't I thought of it before? It sounded so good: 'I'm going to Greece.' I knew no one- this was long before the new Medes, the grockles, invaded -who had been there." Fowles had moved to Dorset in 1965.

"Come to the Greek Islands" (a satirical video aimed at grockles)-  βρωμοτουρίστες

also found on YouTube:

  A poem about moving to a seaside town and being called a grockle