The most common and most likely answer to this crossword clue is the 7 plus 9 letter word STRANGE GOINGS-ON
I've seen this crossword clue in The Times
S
T
R
A
N
G
E
G
O
I
N
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Buddy explains!
The straight part
We know that "funny business" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case funny business = strange goings-on.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.