Boot

Boot(Dutch)translated to English is ship.

Keep your dirty talk on the boot(ship).
Inappropriate conversation in public.

When you talk to your girlfriend at the same way you talk to your friends/colleague's
Sailors talk a lot about dirty stuff.
When your girlfriend tells you to stop talking about inappropriate subjects . She will firmly say the word, boot!

If you say to her: I want to have xxx with you at Christmas dinner table when the all the family is sitting on the same table.
She will just shout, Boot.