There is a point where a useless comparison stops being general and becomes suspiciously detailed, and that is where the good ones live. “A broken kettle” is nothing. “A kettle that boils in forty minutes” is a scene: somebody stood there, watched it, and decided to wait. The extra clause is the joke.
These thirty all carry that extra clause. They are longer than the classics and they take a beat more to deliver, so use them when you have the room’s attention rather than as a throwaway.
Thirty with too much detail in them

- As useless as a left-handed teacup in a right-handed household.
- As useless as the third setting on a two-setting toaster.
- As useless as the second sock in a one-legged trouser press.
- As useless as a Tuesday-only umbrella.
- As useless as a fork with the middle two prongs removed.
- As useless as a jigsaw with the edges missing.
- As useless as a crossword with no clues down.
- As useless as a book with every seventh page blank.
- As useless as a dictionary that stops at M.
- As useless as a piano with the black keys glued down.
- As useless as a guitar with one string and no fifth fret.
- As useless as a metronome that speeds up on its own.
- As useless as a whistle that only dogs from Doncaster can hear.
- As useless as a doorbell that rings in the shed.
- As useless as a smoke alarm that only goes off on Sundays.

- As useless as a thermostat with a range of one degree.
- As useless as a fridge that keeps things at room temperature reliably.
- As useless as a freezer drawer full of ice and one pea.
- As useless as a microwave with a single button marked Maybe.
- As useless as a kettle that boils in forty minutes.
- As useless as a tap that runs only when watched.
- As useless as a shower with two temperatures, both wrong.
- As useless as a bath plug half an inch too small.
- As useless as a towel that is technically waterproof.
- As useless as a hand dryer that blows room-temperature air at your elbows.
- As useless as a car park barrier that lifts for everybody except you.
- As useless as a self-service till that only accepts exact change in coins minted before 1998.
- As useless as a sign that says Sign.
- As useless as a queue system with one number and no counter.
- As useless as a helpline that plays a recording of itself.

Why the detail works
Specific is funnier than strong, every time. The reason is that a specific object forces the listener to build the picture themselves, and people laugh at pictures they built. A dictionary that stops at M makes you imagine looking up “necessary”. A whistle only dogs from Doncaster can hear makes you imagine the dogs. Neither needs a punchline because the audience has already supplied it.
If this is your register, try the forty ways to finish the sentence next, or the complete collection for the shorter classics.