Back again, top dog? I say you are more offensive (5)
I believe the answer is:
ruder
'you are more offensive' is the definition.
I can't tell whether this defines the answer.
'back again top dog? i say' is the wordplay.
'back' is a reversal indicator.
'again' becomes 're' (prefix meaning 'again').
'top' suggests taking the first letters.
'i say' becomes 'ur' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'dog' is 'd'.
're'+'d'+'ur'='redur'
'redur' back-to-front is 'RUDER'.
Can you help me to learn more?
(Other definitions for ruder that I've seen before include "less pleasant in manner" , "More impudent" , "With less warning, perhaps" , "more robust" , "Less mannerly" .)