It's not big of a secret. I dislike Spain because in their 3 consecutive titles run they beat some of my fav teams and I started to despise them for winning all the time and their teams Barca and Real wining almost all the time. There was like 10 years where Spain won everything and made it boring. (yeah, stupid reason). Portugal I don't like because of Ronaldo's ego, and they had one of the most disgusting players I have ever seen. Pepe. Because of that guy I now hate the whole damn country (in football only ofc). Argentina I don't like since child because I never liked Maradona and think he is ECTREMELY overrated.
I'm usually big fan of England, but the recent years their country really fell down in my eyes, and some of their players are just to in love with themselves and grew to big of egos. It is ironic my favorite team in English, when I really don't like England.
Germany is my country in terms of support since child. I just love their philosophy, mentality and teamwork. There is never big egos or huge star to take the shine. It's a team's team.
Well, I almost nailed the reasons then

Your justifications are acceptable for the three teams, though indeed you're basically disliking teams and countries for just one or two reasons... Kinda petty, don't you think?
I for example, can say that France is a personal and probably a general portuguese football hate for a myriad of reasons running through different eras... players, matches, personalities, even a referee! I can remember a bunch of them right of the bat... no hate on all you french collectors here, love you all

But the rest... can't say I have a team or nation I dislike, even if there's one or another reason.
I have a some players I will never like at all... one is Arturo Vidal, I can't stand how he behaves both in the pitch or in his personal life... and yet, I don't despise Chile, quite the opposite, they had a very entertaining team to watch in the past years... Uruguay for example is a team I never liked much, even more with Suarez there, but they have there Cavani (amazing guy imo!) and of course, Seba Coates, Sporting CP captain... not easy to dislike a whole nation when there's also someone to like too.
Speaking of Pepe, I also have a love/hate feeling for him, as I obviously love him when he's the most dedicated player in the portuguese team (and let's not forget he was born in Brazil, but he's more portuguese than most I saw playing for Portugal), but then he has that "hot head", almost killing instinct, which is more visible to me being a club rival supporter (oh yes, I called him some ugly names during Porto matches!)... bear in mind though, he's still the best center-back Portugal had in the past 15 years and maybe the best ever.
Agree with Germany. The moment they start to have some big ego, they crash hard, but quickly overcome.
Btw, I'll hardly ever hate on your country... Told you before, Balakov

Same for Denmark with father and son Schmeichel.