Theatre regularly ignored Friends character? Blow it! (9)
I believe the answer is:
harmonica
'blow it' is the definition.
'theatre regularly ignored friends character?' is the wordplay.
'regularly ignored' indicates alternate letters (letters removed at regular intervals).
'friends character?' becomes 'monica' (I've seen this in another clue).
The alternating letters of 'theatre' are 'har'.
'har'+'monica'='HARMONICA'
(Other definitions for harmonica that I've seen before include "musical instrument" , "An alternative mouth-organ" , "It's played by blowing into holes" , "It's blown" , "Blow me!" .)