As much as the disease is a complete tragedy, these kinda jokes never get old. Even the same joke is fun every time I hear it again for the first time.

What's so insanely cruel about Alzheimer's is that it will not only destroy you, it will test and very often ultimately brake even the strongest and most loyal people around you.
The guy in the German video I posted started hooking up with his wife's best friend who lived with them in the same house, while his wife was still around. This sounds horrible but you can't fault either the husband or the wife's best friend. He admits on camera that he simply didn't have the strength to go on alone and his young son admits on camera that he sometimes thought it would be better if his mom was gone because in a way she was no longer a human being anymore. Who can blame such a sentiment, as shocking as it sounds? I don't think anyone can. Such a burden, unless carried, can't be understood.

Cancer and heart disease were the first two things that came to mind, but as others have mentioned those are actually fairly broad categories encompassing numerous individuals diseases. Ultimately I think I'd go with Alzheimer's, as it currently affects over 30 million people worldwide, is pretty horrible in its ultimate effects, and is also a disease that we probably won't have a cure for any time soon (we still don't know for certain just what causes it, and drugs that have been advanced to the clinic have all failed).

My line of thought was based on the fact that most viruses that I know of are fairly easy to detect relatively early on, and so shouldn't be that difficult to contain. Then there diseases which are much more deadly, but those tend to do a decent job of containing themselves by quite simply killing what whoever they infect. HIV, however...

Can't say I completely disagree.

Alzheimer. Like tinyE & awalterj said in their posts, it isn't only destroying your life but also everyone's life around you.

Lmao.

Cancer. You could have perfect hereditary genes, perfect physical condition, and basically perfect everything but still end up getting cancer simply because you experienced a mutation possibly just from getting older that ended up corrupting your body.

My real hope though is that the human species finds a way to make itself immune to all diseases. I say this because germs and bacteria still have their purposes like decomposing dead matter into soil. Also, should in the off chance the human species experience an alien invasion, the aliens could get wiped out by earthly diseases kind of like in War of the Worlds and if humankind explores outer space and actually visits other planets, nobody has to worry about acquiring or spreading any foreign diseases or pathogens other than the effects they would have on livestock, game animals, and crops.

I haven't a doubt in my mind that we will because history shows we have.

A hard decision to make, as you leave the persons not chosen still affected by their disease, it's almost a tie between depression, schizophrenia, bipolar disorder and personality disorders.

My yardstick? These disorders are rhe cause of enough suffering to lead to suicides in the order of magnitude of about 1 out of 10. I don't know exact figures, but for some estimates see for instance: http://depts.washington.edu/mhreport/facts_suicide.php

I don't know of any physical illness that makes people take their own life rather than contine suffering in such a high degree as the mayor mental disorders. Asto the question what mental disorder is worst, I can't say. Out of my own experience, depression is grueling, but the fear and disoriantion of being psychotic are horrible as well I know, though second-hand.

Any disease that affects the individual experiencing it.

Influenza. Every year it devastates work productivity. I don't know how many people it kills worldwide but in the US about 35,000 die from it every year. Based on that I would assume worldwide deaths top 1 million. The world would be a much better place without it.

The ability to believe societal or self indoctrination in order to directly or indirectly leech/mug/scam others without feeling of guilt.

Apathy. Seriously, it's a disease >_>

Influenza also gets my vote. Everybody gets it and since it mutate fast it strikes and strikes again. Without it humanity would be centuries ahead of where it is now in art, science and technology. No other disease has caused as much lost in human productivity as the flu.

I lost my mother to cancer, I would not wish what she suffered on anyone and I'm likely to die from it as well, but influenza is a curse on all humanity, not just lots of families.

I'm going to be very selfish here but have to say the disease I have had all my life called Minimal Change Kidney Syndrome. We are about 100 people in the world that have it so no one is researching for this specific kidney disease which is very different compared to other kidney problems.

Anyway, if anyone has any questions about it don't be afraid to ask :)