Gibe initially troubling relative (5)
I believe the answer is:
taunt
'gibe' is the definition.
(I know that gibe is a more specific form of the action taunt)
'initially troubling relative' is the wordplay.
'initially' indicates taking the first letters.
'relative' becomes 'aunt' (aunt is a type of relative).
The first letter of 'troubling' is 't'.
't'+'aunt'='TAUNT'
(Other definitions for taunt that I've seen before include "Sarcastic challenge" , "Mock provokingly" , "Wounding jibe" , "Thing said to anger or wound" , "Insult" .)