...was something that a client of ours said to her partner, on Wednesday.
This highlights one of the confusing things about the English language; namely that the same word means different things and the same thing can be called different words in different countries.
If this was in America, then the sentence could have been rendered as:
"My boots are in the trunk in the trunk."
Of course the word 'trunk' in addition to meaning that luggage compartment at the back of your car, as well as a portable sturdy luggage compartment, also means the base of a tree, as well as any centralised system with many branches shooting off; as well as the fleshy hose nose of an elephant.
If you were an actor type thesp, playing a pantomime elephant in a production of 'Dick Whittington' (the second most famous Mayor of London), then you might say:
"My trunk is in the trunk in the trunk."; which is equally plausible both in the wings of the theatre as well as in the actual dialogue of the pantomime¹.
That same pantomime elephant costume might have a boot on the end of its trunk like a kind of puppet:
"There's a boot on the trunk in the trunk in the trunk." or,
"There's a boot on the trunk in the trunk in the boot."
With sentences like that, you actively start to build the lyrics for a music hall type standard; which is probably justified given that you were already an actor type thesp.
If you don't happen to have a trunk in the boot, then having a trunk in the boot might indicate that you are not an actor type thesp but a wildlife smuggler; which apart from the morality of it being quite illegal, is actually quite impressive.
"Putting a boot in the boot" though, is not syntactically all that confusing at all. "Putting a boot in the boot in the boot" means that you are pretty angry with your boot, if you want to kick it².
Perhaps less confusing is that part of the car up front, where all of the enginey things are. This is the part of the car which blokes will open, purely to look at, as of to show that they know things about motor cars; when in reality all they know is the location of the enginey things.
Those enginey things live under the 'bonnet' or the 'hood'; which are both otherwise archaic bits of headwear which you will find on ladies. Just like a motor car, underneath the 'bonnet'or the 'hood' of a lady, are the enginey things which make her go. Blokes have even less idea of what goes on underneath the 'bonnet' or the 'hood' of a lady, because ladies have several layers of complexity going on that men simply do not understand. We do know that that is the location of the enginey things.
If you hear whining coming from underneath the 'bonnet' or 'hood' of either a motor car or a lady, something serious has gone wrong and this means that urgent attention is needed. Sometimes the whining might be caused by liquid hydrocarbon usage.
Likewise, if there is too much junk in the trunk of a motor car, you should probably think about a clean out. If you suggest that to a lady, you had best think about spending the night sleeping in your car.
¹It's behind you!³
²Can I kick it?⁴
³Oh no, it isn't!
⁴Yes you can.