Worst places to retire?   Firstly,

Turkish flag – Best Places In The World To Retire – International LivingWorst places to retire?
Firstly, I note that many responders have replied to a different question- that of living abroad, not retiring abroad. Retirement for those relying on [usually, modest] pension funds poses a different set of issues. My 'standard of living' had to be drastically reduced- but I found many positives from this, including ego-reduction (!) and simplification. Consumerism is now a non-event and life is better for it; the more 'stuff', the more problems.
Taxation, for instance, is likely to be a non-issue without significant income. As the majority of expats are non- US citizens they are not liable for tax on worldwide income AFAIK.
Age- if you are not of retirement age [generally 65+] then your comments may not be entirely relevant. Some countries do not allow retirees to work since this takes jobs from their citizens. Property ownership can again be an issue but it's less common than the jobs issue...
As others have noted, countries that are especially corrupt, lawless and violent are non-starters except for those with a love of danger! My personal number one problem is the Islamic world; as an infidel you will most certainly be at risk in Saudi Barbaria where a casual remark or on-line post will result in jail or worse. I note Saudi law has been updated to make atheism a crime equivalent to terrorism. Women in particular are discriminated against most viciously- don't go! UAE, Qatar, Bahrain and others are heading the way of anti-west sentiment...
Even in the so-called 'moderate' Muslim countries the risks are increasing daily with jihad on the rise; so many people don't understand what is going on, despite daily attacks all over the world.  They are being lied to by politicians and media, accepting the official line about the 'religion of peace'. The Islamic world is in turmoil and exporting its problems- times they are a'changing.
In an earlier piece I wrote of Turkey and its many attractions. Loved living there but the AKP government promotes Islam and opposes secular values, leading to astonishing anti-Semitism. Therefore one begins to fell less secure and wary of what you say in public places, or to people you consider friends.
Even here in Thailand Islam is on the move, from the 'insurgency' in the south to recent bombings in Bangkok and two resort islands. That said, the way things are going in Europe one wonders what the future holds...
Climate- warmth and sunshine are well and good but often tropical areas are worse than cooler places; constant sweating and tropical diseases are not to be ignored. Air conditioning is an expensive alternative to putting on extra warm clothing! Again, increasing age or infirmity must be considered with health costs.
Conclusions- the list of places ideal for retirement is shrinking. Security, corruption, cost-of-living, oppressive regimes... perhaps Cuba might be the next Panama!
(Turkish flag, pictured.)

Best Places In The World To Retire