[i]Either they think that you are being too blunt,[/i]
Too bad for them. I like to think of myself as blunt, and too blunt works just fine for me.

[i]or outright sadistic,[/i]
I'll take that as a compliment :p

[i]or that you are patronizing them.[/i] 
An answer to that would be to the effect of "no, but if that's what you think, you can feel free to go".

[i]When you try to explain that no, they didn't get the meaning of what you said right (which is especially jarring when you use direct language to avoid misunderstandings), they come up with false arguments about you being intolerant and always trying to be on the right (some times appealing to straw man fallacy). Less mature players can actually dive straight for finger pointing and yelling, leaving no room for a civilized talk.[/i]

/kick
0 tolerance for that shit's my policy. I haven't GM'ed in public for a while, and not much on this site, but my general policy is that when people go that route, they can fuck off immediately. I initiate a policy where I ban the fuckers and say that while an explanation can be provided, the decision itself cannot be appealed. Go soft once and you're pretty much done.

It's a scenario unlikely to happen if you trust the fellow coming in and have a good background to work with in the first place. The more you know, the more you can steer from those folks or outright eliminate them upon arrival.