"Fanboy" and "Fangirl" is a term that refers to an overeager and obnoxious fan of a certain franchise who typically ruins it for others.
On its own, there is absolutely nothing wrong with being a fan of a TV/web show you enjoy and show your excitement and appreciation of those shows, the problem comes with certain fans who take it far too seriously. They tend to be obnoxious, complain constantly, overthink everything, reject others' opinions, act authoritative and entitled, refuse to listen, NEVER stop talking about it, feel threatened by people who don't like the shows just as much as they do, make inappropriate fan art, etc. Fanboys/fangirls also tend to blindly defend clearly anti-consumer practices that companies do, allowing those companies to keep getting away with it. Often they'll harass regular fans because they don't agree with their opinions and say the regular fans are "not true fans" sometimes to the point of completely ruining the franchise for them.
Another type of fanboys/fangirls are the "nostalgiatards", who are more prevalent in long-lasting franchises like Transformers and Teenage Mutant Ninja Turtles. These are fanboys/fangirls who believe anything within the franchise besides the classics they grew up with is automatically garbage, worship the classic TV shows like they were perfect and even worse, all of these guys refused to even give the newer TV/web shows a chance.
Perhaps the biggest problem with fanboys/fangirls is that, while they are usually the minority, they tend to be the most vocal and toxic, which in turn makes outsiders think that the whole fanbase is like that and in turn they'll be less likely to give the TV/web shows a chance. However, it should be noted that even if a fanbase is infamous for being full of toxic fanboys, not all of the fans have to be like that. Autovolt is a popular example of a healthy and reasonable Transformers fan.
Just because a show has a toxic fanbase, that doesn't mean the show itself is bad. It is very possible to enjoy a show without being dragged into the terrible fanbase it has.
There is also an article on this topic on the Crappy Games Wiki.
- SJW fans of Steven Universe harassed a Tumblr fan-artist so much that she attempted suicide, simply for the "crime" of depicting the character of Rose Quartz as being thin.
- Another incident is when the fandom accused a writer on the show of encouraging the Lapis/Peridot ship. This led to a writer named Lauren Zuke deleting her Twitter account after non-stop harassment from fans.
- Many anime haters are American cartoon fanboys/fangirls that attack anime fans because they think they're superior to anime fans and think that all anime is degenerate and evil, but turn around and watch hentai. They also call anime fans “weeaboos”, despite not knowing what it actually means, not only that, they also call them that same name all because they watch some shows that are related to anime, in which, it makes no sense at all, and it is also bashing on the "regular" anime fan's opinion.
- The Rick and Morty fanbase is infamous for its dedication to the show and its obsession with gags from the television show. For example, McDonald's brought back the Szechuan sauce (A sauce that was mentioned in the show's third season in which is also the same sauce in the promotion of Disney's Mulan) for one day only. Many fans went to McDonald's locations that had the sauce, and when they found out that there was no sauce left, they started to get angry to the point that, at one McDonald's in Los Angeles, a man was stabbed in the middle of a long line during the promotion, forcing the police to step in.
- The Loud House fanbase is even worse, it contains a lot of Loudcest (in which Lincoln is shipped with his own sisters, even one of whom is the baby, Lily Loud, or has been shipped with other characters into having sexual intercourse, including Ronnie Anne), as well as a large amount of hatred toward some of Lincoln's sisters, especially Lori, Lola (the most hated character), and Lynn (another character who is now panned and despised after "No Such Luck"). There are even racist and offensively unfunny jokes directed towards the Hispanic characters like Ronnie Anne and Bobby Santiago.
- Weeaboos are those who hate all western shows/adaptations and content in preference towards all things Japanese. Especially with anime and tokusatsus. Weeaboos also have a high superiority complex, which is ironic given the culture they love and are actually praising xenophobia, stating Japan is better than all other countries in the entire planet Earth. Also, they blindly defend anime and Japanese tokusatsus on the comment section of videos that criticize anime and American adaptations of tokusatsus like Power Rangers.
- As for tokusatsu fanboys/fangirls, every time there's a new trailer for a new tokusatsu show, mainly Super Sentai and Kamen Rider, they get a bad first impression like how the new show will suck or will get flopped. After watching the first episode of a new tokusatsu show, they get a praise for the show being good.
- The GoAnimate community is filled with users who make grounded videos, dead meat videos, held back videos, baby show error and OS videos, assaulting videos (or punishment day videos), expelled for nothing videos (which is considered a dead topic nowadays), etc. out of real-world people and even worse of all, copyrighted characters from video games and television shows, movies, other users, etc. The community also makes rip-offs of GoAnimate, hate videos out of Alvin Hung, etc. Adamkleinschmidt2003 is probably the most notorious member of the GoAnimate community.
- Elitist Fanboys are those who worship a franchise as if it's some kind of god and look down on fans of other similar shows.
- Parts of the My Little Pony: Friendship is Magic and My Little Pony: Equestria Girls fanbases have been known to send death threats to anyone who expresses their dislike for the franchise and attack other people's opinions all because they took a dislike to the franchise. There's also an ungodly amount of NSFW fanart on sites such as Derpibooru.
- The Thomas the Tank Engine fanbase has been criticized by critics and other Thomas fans on YouTube, since the fans of Thomas still would not let off their hate for Sharon Miller - one of the most infamous writers for the television series. Sure, the overused story plot is aimed for preschoolers, the flanderization of the characters and the rhyming are annoying for fans and critics, but they can't even stop talking about the Sharon Miller era (although, they did have a good reason for how bad it was), even when Miller stepped down from being a head writer after its seasonal rot from season nine to season sixteen. Worst of all, whenever somebody likes or hates an episode, merchandise or movie of the television series, they outright bash and attack them over an opinion and not even get along at all. Not only they complain about Sharon Miller's era for way too long after the series reached back on how they used to be by season seventeen, Mattel is criticized by the Thomas fandom for how badly they made their Trackmaster models in 2014 after Fisher Price's Trackmaster retired in the same year after its five to four year run of merchandising (from 2009-2014), how people in the community felt and thought that Edward, Toby and Henry weren't going to be part of the series anymore as of them becoming former members of the Steam Team when they are still in the television show (possibly/hopefully) just not on the Steam Team after the introductions of newer characters from the upcoming Big World, Big Adventures! film coming soon along with season twenty two coming in 2018.
- The MysteriousMrEnter fanbase is also very toxic, because many of Enter's fans are people that leave hate comments on anti-Enter videos, and blindly defend him no matter how poor his videos are, and one of the ways Enter's fans defend him is by making useless comments saying that Enter is better without a single reason why he is better.
- The infamous Netflix original animated series, Big Mouth, already has toxic fans and it only has one season. The fanbase is quick to harass anyone who dislikes the show. In one instance, one YouTuber commented on the official trailer for the series, claiming that "this show is disgusting, like if you agree". Another YouTube user went to the latter's video (not even their most recent one) and attacked the user who made the critical comment, calling them "immature", and saying they should "go back to watching Hannah Montana". Even though this is only one instance, this could happen to anyone else a second time.
- Some fans can take it way too far. If you don't like a certain show or get into an argument with a fanboy, you could be either assaulted online or in real life.