A few sandwiches short of a picnic – Not very bright.
Barking up the wrong tree – Pursuing the wrong course of action.
As useful as a screen door on a submarine – Completely pointless.
Not the sharpest tool in the shed – Not very intelligent.
Off like a herd of turtles – Very slow to leave.
In the dead of night – Something happening at a very late hour (dark humour twist).
Like a bull in a china shop – Being clumsy or disruptive.
Behind the eight ball – In a difficult or disadvantaged situation.
Bite the bullet – To face something unpleasant head-on.
Dead as a doornail – Completely dead or lifeless (in a dark comedic sense).
A dark horse – An unexpected winner or successful person.
Don't look a gift horse in the mouth – Don't question something freely given.
Jump the shark – To go beyond the point of credibility or fun.
A sandwich short of a picnic – Not completely sane or intelligent.
Get off your high horse – To stop acting superior.
The elephant in the room – An obvious problem no one wants to address.
Till the cows come home – For a long, indefinite period.
Out of the frying pan and into the fire – Going from one bad situation to an even worse one.
Spilling the beans – Revealing a secret.
To cry over spilt milk – To lament something that can't be undone.
Shoot the breeze – To chat casually about nothing in particular.
A wolf in sheep's clothing – Someone pretending to be harmless but is actually dangerous.
Like a rat in a trap – Feeling trapped or cornered.
A fly in the ointment – A small problem that ruins everything.
The skeleton in the closet – A hidden secret, often embarrassing or dark.
Like watching paint dry – Something incredibly boring.
Mad as a bag of frogs – Completely crazy.
A kick in the teeth – A very unpleasant or painful situation.
Put a sock in it – Telling someone to be quiet.
A rolling stone gathers no moss – Someone who is always moving doesn't settle down.
Between a rock and a hard place – In a difficult situation with no good options.
Chasing rainbows – Pursuing an unattainable goal.
Throwing a spanner in the works – Disrupting or ruining something.
A little too much of a good thing – When something becomes overwhelming or excessive.
Grim reaper's holiday – A playful way to describe a particularly ominous situation.
Waiting for the other shoe to drop – Anticipating something bad to happen.
Like a chicken with its head cut off – Running around in a panic or without direction.
In the land of the blind, the one-eyed man is king – In a place of ignorance, a slightly knowledgeable person stands out.
Creeping death – Something slowly but inevitably catching up (used humorously for situations like deadlines).
Like a deer in headlights – Stunned or caught off guard.
Walking on thin ice – In a dangerous or precarious situation.
Flogging a dead horse – Wasting time on something that can't be changed.
You can't unring a bell – Once something is done, it can't be undone.
Curiosity killed the cat – Too much curiosity can get you into trouble.
A wolf at the door – Someone or something threatening or dangerous.
Waiting for the grim reaper – Waiting for something inevitable and ominous.
Like a fish out of water – Out of your element or uncomfortable.
The devil is in the details – Small things can cause big problems.
Like a moth to a flame – Attracted to something dangerous or destructive.
When the shit hits the fan – When everything goes horribly wrong.