Saditty (also known as seditty, hasadity) is an African-American vernacular expression that refers to people who act selfish, snobbish, arrogant, superior or full of themselves.
It was originally said about members of higher social classes, usually.
It’s also primarily used by women, and mostly meant to label other women who appear as “bougie”, or bourgeois in other words.
The etymology of the expression saditty is currently unknown, but there are speculations about it originating from the word “sedate”, which means keeping a quiet steady attitude or pace.
It was developed in the mid-20th century, in dense, urban environments that were populated primarily by working-class African-Americans.
The expression started to appear in print during the 1940s, mostly in articles published by African-American journalists and authors.
It is not used as frequently anymore as in the 20th century, but it is still part of African-American Vernacular English.
There are a handful of articles about saditty found on the website of Urban Dictionary.