Terrible snide outside right cafes (6)
I believe the answer is:
diners
'cafes' is the definition.
(I've seen this in another clue)
'terrible snide outside right' is the wordplay.
'terrible' indicates anagramming the letters.
'outside' indicates putting letters inside (some letters go outside others).
'right' becomes 'r' (common abbreviation).
'snide' anagrammed gives 'dines'.
'dines' going around 'r' is 'DINERS'.
(Other definitions for diners that I've seen before include "Eaters of a meal" , "Restaurants" .)