Insults seeming even worse to a Yankee (6)
I believe the answer is:
rudery
'insults seeming' is the definition.
The definition suggests a singular noun which matches the answer.
'even worse to a yankee' is the wordplay.
I cannot really see how this works, but
'yankee' could be 'y' (phonetic alphabet: alpha, bravo, charlie etc.) and 'y' is found in the answer.
The remaining letters 'ruder' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for rudery that I've seen is " naughty!".)