Little cowboy trick here, y’all:
Don’t bother with “offended” at all. Try unfazed and almost-imperceptibly amused, with an off-color of more pressing things to attend to.
Not to say I have mastered the art myself, but I have seen twelve-year-olds raised on a farm or ranch who handle bad manners better than most folks online ever manage to.
But honestly, what hill of beans does calling folks racist or whatever really amount to, beyond plain ol’ bad manners and ill-brought-uppedness?