I find bland music most offensive. Dull, lifeless bland toss like Buble, Coldplay Will Young, James Blunt and just about everything else on Radio 2. Music is art and art should never be bland.
At least music traditionally seen as offensive has something you remember after hearing it and at least it triggers some sort of emotion even if it's disgust. I feel my time has been wasted if I hear something which just leaves me bored.