Burlesque party in back of downright dingy venue (8)
I believe the answer is:
travesty
'burlesque' is the definition.
(I know that burlesque can be written as travesty)
'party in back of downright dingy venue' is the wordplay.
'party' becomes 'rave' (type of dance party).
'in' indicates putting letters inside.
'back of' suggests the final letters.
'dingy venue' becomes 'sty' (I can't justify this - if you can you should give a lot more credence to this answer).
The final letter of 'downright' is 't'.
't'+'sty'='tsty'
'rave' put inside 'tsty' is 'TRAVESTY'.
(Other definitions for travesty that I've seen before include "Grotesque representation" , "Grossly unfair representation" , "Burlesque, mockery" , "Grotesque parody" , "Absurd representation" .)