The best way to anger Naruto fans is to downplay or ridicule the show itself. Suggest that other anime series are better (particularly the other members of the Big Three), that favorite characters are overrated, or that other characters would beat Naruto characters. Or, point out the weak ending in Naruto.
Some of the easiest ways to anger Star Trek fans are to point out scientific inaccuracies or compare the franchise to other popular science fiction. Even easier, pick a favorite character, ship, or generation and watch arguments go. Basically, express an opinion about Star Trek, and you’ll find an angry fan somewhere.
Asking why a show isn’t in English or why the characters’ eyes are so big are the two easiest ways to anger anime fans. You can also ask a ton of questions, ridicule the medium, suggest that it’s for kids, or misname characters and shows. Or, just point out how unrealistic it is on repeat.
Being dismissive is usually the best way to anger sci-fi fans. You can dismiss their passion as just being “nerdy,” dismiss their philosophical discussion as unrealistic, or dismiss their favorite IP as inferior. You can also annoy them by pointing out problems in the story or mixing up details from different IPs.
The easiest way to anger a Star Wars fan is to pick a favorite movie and stand by it. For some reason, having any preference at all is a sure way to upset the fan base. Beyond that, you can confuse it with other franchises, point out ridiculousness, or misquote the famous line, “I am your father.”
There are three easy ways to anger a Harry Potter fan. Intentionally misname or confuse important aspects of the fiction with things from other universes (like calling Harry by the wrong name). Downplay the emotional impact the story has on fans. Or, suggest that Harry Potter is inferior to other fiction.