The snow was described as being a "show-stopper" on the BBC London News last night. I always thought this phrase was a description of when something is so GOOD that it stops the show (presumably by uncontrollable applause). More and more people tend to use it in a negative form which is not strictly correct.
I think it's a matter of degree: - collision, crash, smash.
A collision is a relatively minor scrape - wing or bumper dented, lamp broken, etc. The car can usually still be driven. Usually only minor if any personal injuries.
A crash is when the structure is significantly damaged, requiring major repair or may be written off. Occupants lucky if they escape injury.
Smash - total wreck, as in head on collision at 80 mph. Car usually unrecognisable, occupants almost certainly killed or very badly injured.
Collision applies to boats or cars, but there isn't really an equivalent for crash or smash. "Run down" is used when a small boat is wiped out by a big one.
I think you argued yourself out of that one. I'm afraid that it isn't a matter of degree. Colliding is what ships do.
The Titanic collided with an iceberg - I don't think you could describe that as a minor scrape!
OK, I tried!
The word collision, in its motoring analogy, is not really a very serious affair, where as I said there is a rough progression in terminology, up to smash or "motorway carnage".
Using collision to cover all marine scrapes somehow does not carry the same resonance, which is why someone hunted around for a stronger word. Of course it is wrong useage, but language should be a tool to communicate, and marine useage here seems to be defficient in the nouns available on land.