De Daumier-Smith's Blue Period
by J.D. Salinger
Mrs. X is a woman Bobby dates. She is present at dinner when Jean tells Bobby he's going to Montreal to teach art school. Young Jean imagines (hilariously) that Mrs. X wants to throw Bobby over for him. It's not entirely clear whether she is actually hitting on Jean or not. As far as we know, she doesn't feature in Jean's life after Montreal.