flatty

(US, slang, dated) A bore; a person who is no fun.

(slang) Flat shoes.

Flatties is a slang term for flat shoes — women's shoes with little or no heel, as opposed to heels or platforms. The diminutive '-ies' suffix gives the word a casual, friendly register. Flatties are associated with comfort and practicality; choosing flatties over heels is often framed as a pragmatic or sensible decision rather than a fashion sacrifice. Used informally in British English and familiar across English-speaking countries. Not negative; the word is straightforwardly descriptive and slightly endearing.