a dirty weekend
A secret getaway in which two unmarried people leave town to have sex. Primarily heard in UK, Australia. When Dana and Harry both skipped work on Saturday, we knew they had gone away for a dirty weekend.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a ˌdirty weekˈend(British English, humorous) a weekend spent away from home in order to have sex, usually with somebody who is not your usual partner: They went away for a dirty weekend in Brighton.
Farlex Partner Idioms Dictionary © Farlex 2017