crashingly

Adverb

Meaning

While crashing, or as if crashing
He stumbled crashingly around the apartment.

Absolutely; terribly

Source: en.wiktionary.org

It is grindingly, creakingly, crashingly obvious that, if Darwinism were really a theory of chance, it couldn't work. Richard Dawkins

I've had a lot of books rejected in my time. My first novel, which didn't get published, was, with hindsight, crashingly dull. Helen Fielding