Lip-curling smile (5)
I believe the answer is:
sneer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lip-curling smile</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sneer that I've seen before include "Show contempt with scornful expression or words" , "Contemptuous expression" , "Speak scornfully" , "Deride, jeer" , "Express cynical contempt" .)