well, although there is an worrying increase of "hate threads"

this is an interesting one:
In terms of domestic results I would normally say FCP but I don't hate them, in fact although a SPorting fan I like seeing Porto win abroad, although they virtually dominated portuguese soccer in the past 25 years.
My "dislike" is somewhat based on other things:
IN PORTUGAL
Benfica - Mainly because of the incident in Jamor, where one of their fans shot one of Sporting fans with a verylight and Benfica never ended their support to No Name Boys and/or demanded for justice. In fact a year ago No Name presented a flag saying "Hugo Inácio és o nosso herói" (Hugo Inácio (the killer) you are our hero". Never saw a single benfica fan speak up against either No Name or this event. (more details here
https://evo-web.co.uk/threads/29409/page-2)
On the other hand I also dislike the arrogant atitude about Benfica. Although they have been pityfull both domestically and abroad (Porto simply dominates both of Lisbon Clubs in all stats since 1975) they speak as if they were still the giant of the 60s and something better than the rest... while they are the first to speak bad of their team and club when things start to go terribly wrong.
The fact that they were the fascist regime club before 1975 (similar to Madrid in Spain) also doesnt ring my bell

.
Boavista - Mainly because of Jaime Pacheco (an ex-manager known for his "phisical" philosophy) and the Loureiro family, who run the club and are believed to be some of the main heads behind soccer mafia in Portugal.
ABROAD
REAL MADRID - Because of the same philosophy of benfica (although Real fans have reasons to speak as a giant in the past decades). The "we are above all the rest" atitude is always a downer for me. I somewhat always liked Barça and Atletico Madrid over Real. The historical background of Real also makes me dislike them, ever since I saw a documentary over the shameful Di Stefano story and Franco's son influence over spanish soccer and mainly favouring Real and damaging Barça.
INTER - I see Inter as a depressive club. A club that is born based on defectors from other club is a bit small in essence I guess. Inter also has become a "player cemitery" in my opinion over the decades, with loads of great players passing by and simply failing to achieve, in a overall depressive environment.
ARSENAL - I tended to like Man Utd in the 27 years "no title" spell and mainly because of the CL run, one of the best I've ever seen (that final...). Arsenal well... dunno why I dislike them but maybe Henry is a problem for me.. I think he is a truly great but the arrogant way he acts, mainly after he scores really pisses me off.
ITALY - Italy is my hated national team (not Greece, who would say hein?

. Since I see soccer Italy always behaved the same way: a hell of a team, with loads of options yet... always opting to play cowardly and not attackingly. I think I only backed Italy in Italia 90, since then I increasingly tended to hate the way Italy's national team faces soccer throughout the tournaments.. they could deliver so much more and they simply don't wan't to.