Tactless about nicer diets (10)
I believe the answer is:
indiscreet
'tactless' is the definition.
(I've seen this before)
'about nicer diets' is the wordplay.
'about' is an anagram indicator.
'nicer'+'diets'='nicerdiets'
'nicerdiets' is an anagram of 'INDISCREET'.
(Other definitions for indiscreet that I've seen before include "Reckless" , "shameless" , "Imprudent -- 10 across (anag)" , "Tactless" , "Too ready to reveal secret things" .)