The most common and most likely answer to this crossword clue is the 9 letter word OBNOXIOUS
I've seen this crossword clue in The Times
O
B
N
O
X
I
O
U
S
More clues leading to the result OBNOXIOUS
- Nasty old boy, nervous, heading off carrying duck
- Old boy with new cow, perhaps, promises to be offensive
- Nasty old coach is receiving no team love
- Vile smell around American seen outside Number 10, repeatedly
- Offensive old boy confronting Number Ten with evidence of debts
- Unusually old bison united with ox in offensive
- Loathsome old boy next door to Number 10 indicating debts?
- Disagreeable old boy’s an infamous doctor with unknown debts
- Clear Number 10 not against being offensive
Buddy explains!

The straight part
We know that "Nasty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nasty = obnoxious.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 OBNOXIOUS mean?
OBNOXIOUS adjective- Extremely unpleasant or offensive; very annoying, odious or contemptible.
- Exposing to harm or injury.