how's your father

noun2

1. •
   (UK, slang) A whatsit; a thing which the speaker is unable or unwilling to specify more precisely.

   • And meanwhile at the station, there's a couple of likely lads Who swear like how's your father, and they're very cool for cats. — 1979
2. •
   (UK, slang) Sexual intercourse.

   • I popped round Mary's for a bit of how's your father.