The most common and most likely answer to this crossword clue is the 3 plus 2 plus 5 letter word CAN OF WORMS
I've seen this crossword clue in The Guardian
C
A
N
O
F
W
O
R
M
S
More clues leading to the result CAN OF WORMS
- Container for angler's bait is a problem
- Bird's preserved food? Could be a problem
- Best not to open this farm — no cows unfortunately!
- Mess that an angler might have had a hand in?
- Frown almost came so easily with a problem
- Potential difficulties with fishing kit?
- Conservative was on form after diverting potential trouble
- Problem coming from wandering cows on farm
- Source of trouble — or likely help to an angler?
- Source for complications developing as from now?
Buddy explains!
The straight part
We know that "Best not to open this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case best not to open this = can of worms.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.