The most common and most likely answer to this crossword clue is the 5 letter word HE-HE
I've seen this crossword clue in The Times
H
E
-
H
E
More clues leading to the result HE-HE
Buddy explains!
The straight part
We know that "a laugh" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a laugh = he-he.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.