Ban a mobile going off — it's atrocious (10)
I believe the answer is:
abominable
'atrocious' is the definition.
(I've seen this before)
'ban a mobile going off' is the wordplay.
'going off' indicates an anagram.
'ban'+'a'+'mobile'='banamobile'
'banamobile' is an anagram of 'ABOMINABLE'.
'it's' is the link.
(Other definitions for abominable that I've seen before include "Hateful" , "Causing moral revulsion" , "Very bad, terrible" , "Atrocious" , "Odious" .)