The most common and most likely answer to this crossword clue is the 4 plus 2 plus 5 plus 5 letter word STEP ON ONE’S CORNS
I've seen this crossword clue in The Guardian
S
T
E
P
O
N
O
N
E
â
€
™
S
C
O
R
N
S
Buddy explains!
The straight part
We know that "upset feelings" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case upset feelings = step on one’s corns.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.