Tango's rejected by toy boy (4)
I believe the answer is:
eddy
'boy' is the definition.
(I've seen this before)
'tango's rejected by toy' is the wordplay.
'tango' becomes 't' (phonetic alphabet: alpha, bravo, charlie etc.).
'rejected by' suggests deleting specific letters.
'toy' becomes 'teddy' (teddy is a kind of toy).
'teddy' with 't' taken out is 'EDDY'.
(Other definitions for eddy that I've seen before include "A small whirl of water" , "Miniature whirlpool" , "movement going round in circles" , "Man" , "current running back" .)