The most common and most likely answer to this crossword clue is the 2 plus 4 plus 8 letter word NO HARD FEELINGS
I've seen this crossword clue in The Times
N
O
H
A
R
D
F
E
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L
I
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More clues leading to the result NO HARD FEELINGS
- Smashed single forehand? I'm not upset
- Number half-resigned after change offering words of reconciliation
- Lacking rigid opinions, I am not offended
- Conciliatory words after spasm of anger’s held in
- In garden with Flo, she prepared still cordial
- Held one’s gran if upset, conciliatory words being required
- NHS freeloading is criminal but offence is not taken
- Single forehand shot and scores are settled
Buddy explains!

The straight part
We know that "I'm not upset" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i'm not upset = no hard feelings.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.