Taproom doubled one's muddleheaded and offensive behaviour (9)
I believe the answer is:
barbarism
'offensive behaviour' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'taproom doubled one's muddleheaded' is the wordplay.
'taproom' becomes 'bar' (synonyms).
'doubled' shows that letters should be duplicated.
'one's' becomes 'i's' (Roman numeral).
'muddleheaded' becomes 'm' (this might be a standard abbreviation I've not previously seen).
'bar' doubled is 'barbar'.
'barbar'+'is'+'m'='BARBARISM'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for barbarism that I've seen before include "Absence of culture and civilisation" , "Uncivilised nature" .)