Pointed remark in pub? Bravo! (4)
I believe the answer is:
'pointed remark' is the definition.
(I've seen this before)
'pub? bravo' is the wordplay.
'pub?' becomes 'bar' (both are drinking establishments).
'bravo' becomes 'b' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' acts as a link.
(Other definitions for barb that I've seen before include "Aggressive remark directed at a person" , "Sharp spike pointing backward" , "part of a habit" , "Cruel remark" , "Jag on a hook" .)