Teases topless partner, an easy target (4,5)
I believe the answer is:
aunt sally
'easy target' is the definition.
(I've seen this before)
'teases topless partner an' is the wordplay.
'teases' becomes 'taunts' ('taunt' can be a synonym of 'tease').
'topless' means to remove the first letter.
'partner an' becomes 'ally' (I am not sure about this - if you are sure you should believe this answer much more).
'taunts' with its first letter removed is 'aunts'.
'aunts'+'ally'='AUNT SALLY'
Can you help me to learn more?
(Other definitions for aunt sally that I've seen before include "Target of general criticism, as in throwing game" , "Family member" , "object of ridicule" , "object of abuse" , "fair game" .)