the feeling that a situation is bad and is not likely to improve.

There's been so much gloom and doom here, I think we should try to provide a smile.

• the fag-end of
• the fag-end of something
• the fairer sex
• the fair sex
• the fat is in the fire
• the feathers fly
• the final curtain
• the final straw
• the fine print
• the [first/highest/next etc.] rung on the ladder
• the first rung on the ladder
• the first string
• the first thing
• the first thing in the morning
• the flavour of the month
• the four corners of the earth
• the four corners of the world
• the ... from hell
• the front office
• the fruit of loins
• the fruit of your loins
• the full monty
• the funny thing is
• the fur flies
• the game's up!