Incomprehensible expressions

[Dilbertian]

I think I've worked out what these mean, but why do they mean that?

Crickets - silence
Fill your boots - if you like
Lose your rag - lose your temper
Go postal - do something in anger

Have I got them right? And why do they mean what they mean?

Please also post any expressions that puzzle you!

Crickets is presumably because it's so quiet you can hear the crickets chirp.

The postal one refers to postal workers in the US losing their rags and shooting up the place

Surely it's too tasteless to use?

Crickets are to emphasise there are no people talking. Silence, in which you hear the crickets chirp.

And no, the PP is right, it was the cliché that the crazy guy in the clock tower shooting people is a postal worker.

There’s even a bit about it in the Steve Martin film Parenthood.

I've always known 'fill your boots' to mean 'eat as much as you like'.

Wiki

Keep an eye out for something - looking out.

If your eye is out, surely you can't see...

Fill your boots means to do/take as much as you like of something - which included but is not limited to food.

Miners used to fill their work boots with coal at the end of the day and carry them home.

‘Shoot the breeze’ is one that’s popped up a lot recently.
I prefer to think that ‘fill your boots’ relates to looting in time of war: carrying off everything available in anything available.
I’ve never heard ‘crickets’.

I thought ' fill your boots' has the same source as 'bootleggers': illegal booze being hidden in smugglers' wellie boots.

I think ‘fill your boots’ is a British expression whereas ‘bootleg’ is American in origin.
I can see ‘fill your boots’ being used in a ‘Whisky Galore’ sort of situation.