The most common and most likely answer to this crossword clue is the 4 letter word JIBE
I've seen this crossword clue in The Times
J
I
B
E
More clues leading to the result JIBE
Buddy explains!

The straight part
We know that "sneer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sneer = jibe.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 JIBE mean?
JIBE noun- A facetious or insulting remark; a jeer, a taunt.
- To reproach with contemptuous words; to deride, to mock, to taunt.
- To say in a mocking or taunting manner.
- To make a mocking remark or remarks; to jeer.
- To accord or agree.
- Alternative spelling of gybe
- Alternative spelling of gybe