Things you CANNOT do

Nana3 it was said that Her Majesty made a mountain out of a molehill when she made the diminutive Antony Armstrong-Jones into Lord Snowdon.

You cannot:

Have your cake and eat it too.

Be joined at the hip.

Have a baptism of fire.

You cannot:

Cry your eyes out

You cannot:

Be born with a silver spoon in your mouth

my current "beefs" though perhaps not completely this thread

twice .. seems to have disappeared from the English language, everything (well nearly everything) is two times..

and you and me.... now everyone, ! says me and you... I was taught to always put the other person first,,, perhaps language follows how people behave?

laugh your socks off

lose your appetite and find a horse’s

(........) until the cows come home

Meet yourself coming back.

Climb every mountain (although Munro collectors try hard)

Well it is Pedant's Corner Magrithea!

I don't think it really matters that the title is not quite specific enough. Phoenix has clarified exactly what she meant, by offering examples to start us off. We understand what she means, otherwise there wouldn't be so many responses.
It's intended to be a lighthearted thread, which I've thoroughly enjoyed reading. Thanks Phoenix!

Turn green with envy

Scramble your brains, OP!

My mum says I can hear the grass grow.

Am I being a pedant by saying that these are all figures of speech, not things you can actually (lietrally?!) do?

Would die for

Jump from the frying pan into the fire (unless it was a huge frying pan!)

Your heart-strings cannot be tugged.

Sleep on the head of a pin

Drive someone up the wall.

Have cloth ears.
Die of embarrassment.
Turn green with envy.
Keep it under your hat, well not if it is a secret,

...or seven sheets to the wind.

You can't be as drunk as a skunk, or as pi**ed as a fart.

Have feet of clay
Or a tin ear
Or a mouth like the bottom of a birdcage
Or turn the air blue although I've given it a good go

Laugh your head off.