Disclaimer: I'm Slovene, living in Slovenia, and for all the practical purposes, I don't hate USA.
That being said, you need not to think our nation bears some deep, jihad-worthy hatred, that might result in attacking tourists or other acts, not worthy of civilized beings. It is more an annoyance, or even frustration. it comes down to many reasons.
1: As we gained our independence, we were set on the path of European integration, finally joining the EU and NATO. there were some skeptics, but the majority expected, that our quality of life will increase significantly, even unrealistically so - comparing us to Switzerland, Luxembourg, Sweden or Norway. The best countries in the world, in fact. Ironically, this is kinda true. We're member of OECD and belong to top 30 countries in the world. And this leads to...
2: We Slovenes are the epitome of the popular "High Expectations Asian Father" meme.
We are never pleased with results, always wanting more. As for anecdotal evidence, in season 2012/2013 Slovenian alpine skier Tina Maze won the overall World Cup, with record number of points. Yet there were still people belittling her achievement as a fling (mainly because her main rival, Lindsay Vonn injured herself), and that she should do it ALL THE TIME, or she's not good at all. This mentality is so ingrained in our lives, that we're not content with anything. So, our opinions about everything might come up as negative.
3: Thanks to the media, we, and the rest of the world are constantly bombarded with stories about American stupidity. You know, redneck accidents, dumb laws and lawsuits, bad reality shows and such. We are not alone in this, as stereotype about stupid, loud, gun-wielding Americans watching Honey Boo Boo and Jersey Shore goes pretty much worldwide. But, it goes a bit deeper. in 20 years of independence, all those things started to creep into our, post-socialist culture. It is not, that similar things weren't present before, but the government worked hard to hide or suppress them, as we needed to appear a successful, smart, and highly moral society, superior to decadent West. And you know what? The main reason for so-called Yugo-nostalgia is that feeling, that we were smart, moral and successful, and now all the values are going to hell.
And with that, we are turning into a tiny version of USA. A lot of us find that thought really disturbing. Instead of picking up the best things from the West, we are really picking the worst ones. We're picking tycoons, high unemployment, social inequality (ironically, we're No. 1 in Gini index of the world equality!) and conspiracy nuts like chemtrails. This is not true, of course. Those things were always there, just covered up. Now, with the power of media and internet, they are made glaringly public. And that brings me to the final point.
4. Instead of solving the problems, we really like to find someone to blame, and shifting the responsibility from us to the others. Be it our corrupt politicians - Right now we are living in a some kind of surreal version of House of Cards, with our own Underwoods and Tafts ("Uncles from behind", Puppet masters, etc). WE blame EU for not being what we thought it would be, and we blame the whole world for not recognizing our greatness, our entitlement to whatever we think we deserve. And USA, as a major superpower is just as fine scapegoat as anyone else.
But no, we don't really hate America, or Americans, for that matter. If you visit us, we'll welcome you, treat you as a dear guest and make everything to feel you comfortable and make you love us. Because that's who we are. A tiny, extremely self-conscious nation, struggling with its own identity. We are a teenage country, confused with the world and not yet finding our role and place in it. We feel bullied, unappreciated, and think that nobody understands us.
Yet, I know, we will grow out of it.
