The quote, which seems to capture its author's reckless personality perfectly, has been misquoted and misattributed. There are a dozen variations of it across the internet. The questions I had were, which version is correct and where is it from?
If, like me, you guessed he said it in his younger years and bought the popular abridgement of his early works in a bid to find it, you will be disappointed, for that edition omits the passage that contains it altogether. Finally I have found the answer:
"Nothing in life is so exhilarating as to be shot at without result."
You can read the quote in context here: see page 107. It may be that, given that the book is based on a series of letters Churchill wrote to the Daily Telegraph to describe the fighting that in fact that newspaper was the first to print it.