What it means
Dirty laundry is the messy private stuff people usually don't want out in the open: family drama, embarrassing rows, old scandals, all that grubby business. If you air your dirty laundry, you put those secrets on display for everyone to stare at and have an opinion on.
Usage examples
"Let us not air our dirty laundry in front of the guests."
"They aired all their dirty laundry in a very public and very messy divorce."
"She aired the family's dirty laundry on national television and her relatives haven't spoken to her since."
"I don't want to discuss the divorce at the office Christmas party, no point in hanging out the dirty laundry."
"Mate, save the dirty laundry for home, yeah? The whole pub doesn't need the family director's cut."
Where it comes from
It comes from the older phrase wash your dirty linen in public, which shows up in English by the 1800s and was likely reinforced by the French saying laver son linge sale en famille. Later, dirty laundry became the punchier everyday version, especially in American English.
