Beyond the pale
As in: "Assad fluffed his chance. Now he has gone too far. He is beyond the pale. Britain and its allies should break with him - and demand he step down." (The Guardian, May 9, 2011)
Comes from: The same root as 'palisade'. The pale is a barrier of safety between you and the enemy -- being beyond it is to be truly the other. And not only a stranger, but a threat as well. On the other side of the wall, literal or here figurative, lies a group intent on breaching your fortifications and destroying you and your way of life.
Severity - 9/10: If you've earned this distinction, you almost definitely fit the profile of a man who has lost his gosh-darned mind. At least in the mind of the speaker. But it feels more like a location-marker, literally, than an emotional revulsion, more aseptically academic than viscerally offended.
Haughtiness - 4/10: This isn't a term reserved for the lower classes or the uninitiated, as the above example shows. But it is addressed to an educated audience, those in a position to judge behavior from an esteemed vantage point located most indubitably inside the pale--like the op-ed pages of a London broadsheet.
Usage guide: You're probably just showing off--linguistically peacocking--if you use this phrase. But +5 points if you work in the time-honored straw-man political construction of "but (opponent), for whom (sensible policy) would be beyond the pale, clearly just doesn't understand (constituency)."