"As for the term "coloured", a related word n****r I hear being used.
But, most of the time when I hear it used, it's not meant for African
people. It's used to describe someone who is lazy, dumb, and ignorant.
I referred to a white man as a n****r before, because he was lazy
and stupid. I hope no one takes that as an offense." maple_leaf_boy

Well, yes. I would take offense at it. Think of it as 'circular'.

Black people used to be called that and the implied meaning was that they were 'lazy and stupid (and worse).

So, if I call a white man by that word implying that he is lazy and stupid, I am applying a word that *used* to mean a lazy and stupid people. I am going along with the original meaning, saying that he is no better than they.

I'm not sure I'm making my reasoning clear. Suffice it to say that yes, I would find it offensive whether or not the speaker meant it so.