The only countries I've actively disliked being in at the time I was there, and wouldn't want to go back to under any circumstances, were the US and India.
There are several places where I lived and worked, and travelled to, in the 60s, 70s and 80s to which I'll never return, as the situation in them is so changed that a return to them would be all but impossible. I liked them well enough when I was there, though. Then there are the countries I lived and worked in, and visited, in the late 90s and for the 10 years following - Australia, New Zealand, New Caledonia and several South Pacific Islands. Simply too far away, although I'd go back like a shot - especially to New Caledonia! - if travel were all of easier/faster/more affordable/eco-friendly.
I'm not at all familiar with sub-Saharan Africa, Central or South America or China, but I've been to big chunks of the rest of the world - often for work - and I've liked lots about almost everywhere I've been.