Mock relative attending tango (5)
I believe the answer is:
taunt
'mock' is the definition.
(I know that taunt is a type of mock)
'relative attending tango' is the wordplay.
'relative' becomes 'aunt' (aunt is a kind of relative).
'attending' says to put letters next to each other.
'tango' becomes 'T' (phonetic alphabet: alpha, bravo, charlie etc.).
'aunt' put after 't' is 'TAUNT'.
(Other definitions for taunt that I've seen before include "Make fun of" , "Tease hurtfully" , "Provoke; tease" , "Mock, jeer" , "Mock provokingly" .)