Professor's lectures likely to offend (6)
I believe the answer is:
coarse
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for coarse that I've seen before include "Rough, uncouth" , "Rough or crude, lacking refinement" , "Rought or crude" , "Unrefined; rough" , "gross" .)