Racket about messy bistro (5)
I believe the answer is:
diner
'bistro' is the definition.
(thesaurus)
'racket about messy' is the wordplay.
'racket' becomes 'din' (both can mean a loud noise or disturbance).
'about messy' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'din'+'er'='DINER'
Can you help me to learn more?
(Other definitions for diner that I've seen before include "US cafe" , "US eatery" , "American cafe" , "Small US restaurant" , "one taking several courses" .)