Cause irritation right on the joint (6)
I believe the answer is:
rankle
'cause irritation' is the definition.
(I've seen this before)
'right on the joint' is the wordplay.
'right' becomes 'r' (common abbreviation).
'on' means one lot of letters go next to another.
'the joint' becomes 'ankle' (ankle is a kind of joint).
'r'+'ankle'='RANKLE'
(Other definitions for rankle that I've seen before include "Cause long-term irritation" , "Continue to vex" , "Stick in one's craw" , "Cause persistent annoyance" , "Chafe" .)