Hanky panky
British SlangDefinition
Playful or illicit sexual activity; also suspicious or underhanded behavior.
Examples
"The landlady frowned and said there’d be no hanky panky in the spare room, thank you very much."
"The auditors are sniffing around; any financial hanky panky will land them in hot water."
"He thought he was being subtle, but the whole pub clocked the hanky panky going on by the jukebox."