Marianne Jean-Baptiste says that she’s playing “the ultimate Karen” in Mike Leigh’s new film Hard Truths. The character’s name is, actually, Pansy. The horticulturalists at the Royal Botanic Gardens in Kew, just outside of London, describe the Pansy flower as a symbol for “humanism.”

That’s not a description Jean-Baptiste would recognize in the Pansy she plays in the movie.

She smiles as she relates how the character she and Leigh created after intense discussion and rehearsal “as a combination of five different women, all of whom had the milk of human kindness removed from them.”

That’s a perfect summation of Pansy, a fastidious woman, who keeps the North London house she shares with her plumber husband Curtley (David Webber) and Moses (Tuwaine Barrett) as their unmotivated son, spotlessly clean.

She’s particularly fixated on polishing her leather couch.

Her family, including her sister Chantel, played by Michele Austin,...