PIECE DE RESISTANCE

What is the meaning of this phrase? I remember a pub bore telling me it was French for Torture Chamber - "piece" meaning room, and "resistance" referring to the resistance of the person being interrogated, which presumably would be overcome through torture. Is there any truth to this?

No. It is much simpler than that - it means a piece (or article) of (or with) staying power, longevity or the like.

DFG

Your pub bore had come across a hoary joke genre called "Fractured French", and either had failed to realise it was a joke, or was pulling your leg with it. "Fractured French" consists of (mildly) amusing skewed translations of stock French phrases, as in the following:
Coup de grace - lawnmower
Tant pis, tant mieux - Auntie spends a penny, Auntie feels better
J'y suis, j'y reste - I'm Swiss and I'm staying
Moi aussi - I'm Australian.
and so on and so forth. (VSD)