Writing the recent post on helmets reminded me of an incident with a cheap helmet many years ago, which convinced me that helmets, however cheap and nasty, are very strong and highly likely to save your bonce if you ever go arse-over-tit.
When I had a bike as a student, back in the Napoleonic Wars, I only had one helmet - the cheapest I could get, as I was an impoverished student on a grant (yes, that long ago) of £305 per term . However, if I needed to carry a passenger (like a girl, perhaps?), I would need another one. A friend sold me an old one that he no longer used; I think I paid 50p for it. It looked a bit like this:
only this one was a lovely pea-green in colour, and rather battered. I couldn't stick the green, so I sprayed it black and carried it everywhere (well, you never know ...). It was worn by several lady passengers, and eventually by the future Mrs GFGN on a tour of Southern Ireland. It must have done thousands of miles either strapped to my pillion seat or rattling around inside a top-box.
After a while, I started to have a conscience about this. For one, it was second-hand, and everyone knows that second-hand lids are dangerous. One drop on a hard surface and a helmet is scrap, and if you don't know its history, how can you be sure it hasn't had its one fall already? And for two, everyone also knows that cheap polycarbonate helmets (of which this was a shining example) are weakened by the adhesive in stickers and by spray paint. This one had had the lot. I finally decided that it didn't owe me anything, and that I should get rid of it. But the responsible person doesn't just throw it away, as it may be picked up by someone else and used, and if they had a crash and died it would be sort of your fault, and ... you know what I mean. So I decided to smash it into pieces. After all, with all that damage and weakening, it couldn't be difficult, could it?
I hit it with a hammer. The hammer bounced off. I hit it hard. The hammer bounced off violently. I hit it with a 2lb lump hammer. The hammer rebounded and damaged my wrist. I put it on the floor and stamped on it. I nearly broke my ankle. I am not a small chap, never have been, but I can honestly say that I put all my weight and all my strength into destroying that helmet. I took most of the paint off, right enough, but I couldn't do anything to the structure beyond scratching it. Eventually, I took the intelligent way out and sawed it in half.
If you were wearing that and went under an 18-wheeler, I can guarantee that you would be strawberry jam, but the helmet would just ping out from under, land in a tree, and be good for another 20 years. Lesson - even the cheapest helmets are stronger than you would believe.
 And I finished my first term with 2p in my pocket, having had to hitch-hike across the Pennines. No student loans then. I was proud; Dad was furious. He reckoned I should have been able to save something out of all that money.