The most common and most likely answer to this crossword clue is the 8 letter word LOUSIEST
I've seen this crossword clue in The Daily Telegraph
L
O
U
S
I
E
S
T
Buddy explains!
The straight part
We know that "Worst" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case worst = lousiest.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.
What does LOUSIEST mean?
LOUSIEST adjective- Remarkably bad; of poor quality, dirty, or underhanded; mean, contemptible.
- Infested with lice.
- (usually with with) Filled or packed (with something, usually bad).