bitch about sb

bitch about sb and have a bitch about sb (to complain or make unkind remarks about someone or something, especially about someone who is not present) — перемывать косточки; сплетничать; судачить о ком-л.| жаловаться, высказывать недовольство

Example 1: Who are you two bitching about now? — Кому сейчас кости перемываете?

Example 2: You can rely on them to bitch about their boss at every available opportunity. When the boss isn't here they usually sit around and bitch about him.

Example 2: Yesterday we had a good bitch about work.

Usage note: the phrase is not rude and has nothing to do with sex. It's just about complaining.