The most common and most likely answer to this crossword clue is the 6 plus 3 plus 4 letter word BEYOND THE PALE
I've seen this crossword clue in The Daily Telegraph
B
E
Y
O
N
D
T
H
E
P
A
L
E
More clues leading to the result BEYOND THE PALE
- A boy, ten, helped out? That's totally unacceptable
- Intolerable and badly done-by, help mate with no source of money
- Developing polythene bead is unacceptable
- Intolerable — badly done by friend pinched by you once
- Deeply hate nob, horribly unacceptable in behaviour
- Unacceptable, but past help, ate out
- Telephoned by a drunk? That’s unacceptable
- Fancy a blonde type? He is unacceptable!
- Outrageous hype, belated hustling carries on
- Unstable Yankee with blonde pate, he’s unacceptable
Buddy explains!
The straight part
We know that "unacceptable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unacceptable = beyond the pale.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.