Japan - Hideki Tojo, who led Japan to failure in WWII
Russia - Feodor the Bellringer, completely crazy son of the the mostly crazy Ivan the Terrible. Spent most of his reign walking around Russia ringing bells. Last of the proper Rurikid dynasty (to actually rule Russia, at least)
Russia - Peter III. Most know him as basically the punchline of the Seven Years' War, before being assassinated by his wife, Catherine the Great, that's why I put him here. In reality though, he could have possibly been a pretty good ruler of Russia, deciding to ally with Prussia rather than with Austria is a rather good idea, but he sadly got assassinated by Catherine before he got his chance.
France - Charles VI the Mad is definitely my first choice. Leading the country between two pretty decent kings, one of which, Charles V, had practically already won the Hundred Years' war before Charles VI screwed it up, and then his son Charles VII had to pick up the pieces. Do I even need to mention his madness?
France - Adolphe Thiers. This is more of a personal hatred for him then anything else. Back in 1840, he was prime minister of France (I believe, or someone really important in France), and egged on France to annex the Rhineland, causing unnecessary strife in a country full of it (although demanding the Rhineland did get Germans to write a pretty cool song). Then, in the aftermath of the Franco-Prussian war, Adolphe Thiers led France and massacred the citizens within the Paris Commune.
Austria - Franz Joseph. The guy who oversaw Austria go from a Great Power to basically disintegration (almost, not quite, he was just 2 years off from that mark)
Spain - Charles II. While I don't quite know enough about his rule personally, I do know that it ultimately led to the War of the Spanish Succession (not quite 100% his fault, I don't think we can really blame him for being impotent. We can blame him for being incompetent though!)
Denmark - Christian VII, the fapping king. Oh, he's hilarious
Denmark - Christian II the Tyrant. Hated in Sweden, and as far as I know he isn't anyone's favorite in Denmark or Norway either.
Zulu - Shaka. In many ways, Shaka is both the best and worst leader in Zulu history. He founded an empire, yes, but he also did so very brutally, and in founding an empire he caused a massive, disastrous upheaval in the region (so much so, that period is pretty much called The Upheaval). Later, he would go crazy and kill a lot of people in his country.