The most common and most likely answer to this crossword clue is the 4 plus 4 letter word BOOM BOOM
I've seen this crossword clue in Independent
B
O
O
M
B
O
O
M
More clues leading to the result BOOM BOOM
Buddy explains!

The straight part
We know that "as joke ends?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as joke ends? = boom boom.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.