the.com/lace curtain

means Describes a style of respectable, aspiring-middle-class status (especially among Irish-Americans) marked by genteel manners and a determination to seem a cut above one's rougher origins.

from From the literal lace curtains hung in windows — a cheap, lace-making-machine-era way to dress up a modest home and signal refinement to the street. The phrase 'lace curtain Irish' emerged in American English (roughly late 1800s–early 1900s) to distinguish upwardly striving, decorum-minded Irish immigrant families from the unflatteringly-labeled 'shanty Irish.' The curtain itself became shorthand for the whole performance: thin fabric, thinner pretense, hung up for the neighbors to see.