The most common and most likely answer to this crossword clue is the 2 letter word TE
T
E
Buddy explains!
The straight part
We know that "expressing derision" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expressing derision = te.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 TE mean?
TE noun- In solfège, the lowered seventh note of a major scale (the note B-flat in the fixed-do system): ta.