curtain-twitcher
informal noun phrase

- A nosy person who watches his or her neighbours, typically from a curtained window (Wiktionary)

- a person who likes to watch unobserved what other people are doing (Collins)

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ORIGIN

This phrase can be traced back to early Victorian homes with bay windows that let in a lot of light and which often included fitted window seats.

Previously, curtains (or drapes as Americans still call them) were heavy and sound-deadening, and with excellent insulating properties.

The combination of drapes, lace curtains and a comfortable perch formed the domestic equivalent of a birdwatcher’s hide and provided the means to spy on passers-by in the most genteel way - a temptation that proved irresistible.

Hence the term ‘curtain twitchers’ for nosy neighbours and, not at all coincidentally, the equivalent term for obsessive birdwatchers, commonly called ‘twitchers’.

In marked contrast to the UK past and present, residents of Amsterdam streets of similar houses invariably have no curtains or blinds, thus affording perfect views in and out - suggesting to all observers that the inhabitants lead a blameless life.

(Thanks to Keith Allum)

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SYNONYMS

busybody, buttinsky, chatterer, eavesdropper, fink, fussbudget, gawker, gawper, intermeddler, newsmonger, nosy parker, pryer, sidewalk superintendent, interfering person, nosy person, meddlesome person, nosy neighbour, intrusive neighbour, prying neighbor, prying person, gossip, interferer, rubberneck, scandalmonger, snoop, snooper, tattletale

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SMUGGLE OWAD into a conversation,
say something like:

“CURTAIN TWITCHER is a lovely term to describe a nosy neighbour.”