Finaly a defnintion that makes sense.
I would just like to add my own $0.02 to MacInnes' working definition, which is probably the best one I've come accross so far. I don't think it can be stated strongly enough; "the powerful and rich should be subjected to greater mockery than the poor and underprivileged." You do not mock those who are less fortunate than yourself. You don't take the piss out of kids with Downs Syndrome - the world has already given them one of the shortest ends of the stick it has to offer, and they have quite enough in their lives to struggle against without "transgressive" "commedians" perpetuating further prejudice against them. Same goes for anyone who's been dealt a crappy hand in this world. How fucking childish is that kind of behaviour? Worse than childish. Seriously - if you had kids, and they started making fun of the one kid in the playground with learning difficulties, or the one with one leg, or the one Indian kid, you'd be horrified, and your kid would be grounded for the rest of his/her natural life. We punish children for this kind of behaviour, and yet laugh at adults who should be old enough to do better? No. Not funny, Frankie.
At the same time, I think it's also a question of relative power - not an absolute. Essentially - it's ok to make jokes when you are doing it compassionately, and from a standpoint where your privilege is not making you into a patronising git. As an example - Eddie Izzard joking that there are benefits to being dyslexic - because it meant you were a killer at I-Spy... "'S' is for 'Ceiling!'" etc. I have heard some really great jokes that were teetering round a whole load of -isms, but which managed to be handled properly and in an empowering way. The problem comes when straight, white, able-bodied men (and most of the time it is S,W,A,M, but I feel forced to add "or anyone else in a position of privilege" just to cover the small percentage of cases when it isn't) decide to make comments about a minority without knowing what the fuck they're talking about. They haven't lived it, and they haven't a clue how to handle it. That's not "alternative" - that's the dominant perspective. And again, that's not funny.
I will however leave you with something that is funny. Courtesy of my mate Nik who sent me the link. And who also has some insightful questions on the original subject here.
And something that will definitely make you smile, even if you didn't like the above.