humorous

sexual activity, especially when it is secret.

You're looking very tired these days, Ron. Been indulging in too much extracurricular activity?

• a femme fatale
• a fender bender
• a few fries short of a Happy Meal
• a fifth wheel
• a fifty-fifty chance
• a fight for life
• a fighting chance
• a fig leaf
• a figment of imagination
• a figment of your imagination
• a figure of fun
• a fine kettle of fish
• a fine line
• a finger in every pie
• a firm hand on the tiller
• a fishing expedition
• a fish out of water
• a flash in the pan
• a flight of fancy
• a flight of fantasy
• a flight of imagination
• a flip-flop
• a fly in the ointment
• a fly on the wall
• a fool and his money are soon parted.