It's awful 'cos it's rude and tacky, ultimately? (11)
I believe the answer is:
discourtesy
'it's' is the definition.
I can't judge whether this definition defines the answer.
'awful 'cos it's rude and tacky ultimately?' is the wordplay.
'awful' indicates anagramming the letters.
'and' says to put letters next to each other.
'ultimately?' suggests the final letters (I've seen 'ultimately' mean this).
The final letter of 'tacky' is 'y'.
'cos'+'its'+'rude'='cositsrude'
'cositsrude' is an anagram of 'discourtes'.
'discourtes'+'y'='DISCOURTESY'
Can you help me to learn more?
(Other definitions for discourtesy that I've seen before include "A rude lack of consideration for others" , "incivility" , "Rude behaviour" , "Ungraciousness" , "terrible rudeness" .)