Crossword Genius

It's forbidden being mean online, but nasty (13)

Ross

I believe the answer is:

unmentionable

'it's forbidden' is the definition.
(thesaurus)

'mean online but nasty' is the wordplay.
'nasty' is an anagram indicator.
'mean'+'online'+'but'='meanonlinebut'
'meanonlinebut' anagrammed gives 'UNMENTIONABLE'.

'being' acts as a link.

(Other definitions for unmentionable that I've seen before include "Forbidden as a topic of conversation" , "Not fit to be referred to" , "Taboo" .)

I've seen this clue in The Telegraph.
Want a hint initially instead of a full solution? Install my app