This obviously isn't referring to all of their fans since I'm one myself and I don't consider myself stupid :P I also don't mean most of them but enough to give the rest of us a bad name. These are the ones you want to avoid online.
Batman
This might be surprising coming from me since he's my favorite comic book superhero, but he has does have a lot of fans who believe that he would beat literally anyone with prep time just because he's Batman. These are the ones with Batman Syndrome.
The Superman example given above is the most common one since many of them say that Batman always beats Superman, but Superman has won pretty much every canon fight they've had and majority of the non-canon ones too (I already mentioned this in my Superman take). You'll also hear them say that Batman is the only one who can beat Superman, but there have been many characters who have beaten him more times than Batman. 
This isn't just limited to arguments about Superman. That was just one example. There are fans who believe that Batman can beat anyone with enough prep with no reason other than "He's Batman!" (Okay... I love that phrase too, but let's be realistic). That even includes the person writing the comic 😒
Deadpool
His popularity has gone up a lot after the movie came out. Close to half of his fans probably haven't read a comic featuring him. I don't see a problem with this since not everyone reads comics, and I don't expect them to either. However, there are fans who think that they know all about the character just because they've seen one movie, even though they didn't know about him last year.
Unpopular opinion: The movie was meh.
I did enjoy it, but it's not a movie I'd pay to go watch (and I'm glad I didn't tbh). Not just for a superhero movie but even for a comedy. Most of the jokes weren't even funny. I'm just glad they got his character and backstory right, unlike the mess that was X-Men Origins: Wolverine.
Hulk
There are people who say that Hulk is just an angry monster with no personality. I disagree because I think he's an interesting character and has some of the best stories (Planet Hulk, World War Hulk, and Return of the Monster; just to name a few). I've heard many fans use the argument "Hulk wins because he has unlimited strength." though. Now it's true that Hulk has absolutely no limits to how strong he can get and he even has an extremely fast healing factor that makes him almost impossible to kill.
But these abilites are only useful when he's in a physical fight. I've heard people use that argument even for characters like Franklin Richards, a character who can literally change history to prevent Banner from becoming the Hulk.
But he's got limits even when it comes to his physical attributes... Fun fact: Hulk has admitted that the reason he prefers to jump is because his legs can't run fast enough.
Superman Prime One Million
I've heard a lot of mixed opinions about Superman. People often say that he's overrated, overpowered, and that his only weakness is a green rock. I personally disagree and feel that he's underrated. He's one of my favorite characters. Now Superman Prime One Million is one of the most powerful versions of Superman, but he's pretty much featless. Because of this, people in battle forums give him feats that he's never performed and use him as an argument against any other character. 
What he can do
For those of you who know about Superman's abilities, you probably know that he gets his powers from the sun. Now Prime One Million is a version of Superman that was sun dipped for 15,000 years. So all of his attributes have been enhanced billions of times. So he's billions of times stronger, faster, and more durable than he usually is. I don't want to spend this take doing the math but you can read more about it here. 
Being sun dipped for a few days also makes Superman immune to kryptonite for a short amount of time. So this version is also immune to kryptonite for... probably a decade.
What he can't do
The feats that a lot of fans seem to give him are usually based on dialogues he said that are usually taken out of context. I've heard people say that he can create new universes, resurrect dead people, create life out of nothing, or that he's immortal. None of these are true. A friend of mine actually debunked all of them here.
Basically, a sun dip only enhances the abilities that he already has. It doesn't give him any new ones. The only real difference is that he's immune to kryptonite, but even that's not permanent. However, he's not the most powerful version of Superman (despite what some fans might tell you). It's actually Cosmic Armor Superman. Don't even get me started on his abiliies.
Storm
This used to be the case 4 years ago on many comic book forums like Comic Vine or CBR. Those fans seem to have disappeared now but you still find them occasionally. A mere mention of Storm was sometimes enough to get these fans worked up into a frothing frenzy and any insinuation that Storm is somehow not perfect or is lesser than another character in some way was met with a ravenous desire to crucify you with misinterpreted scans and wildly inaccurate claims about her power set. 
She's a great character. In fact, she's one of my favorite from the X-Men. However, she's not an omega-level mutant. Fans continue to insist that she is one even though Marvel's handbook clearly states her as Alpha-level. It does say that she has an omega-level potential, but not that she is omega-level.
When I used to go on Comic Vine 4 years ago, the Marvel section was pretty much filled with vs. battles about her and other characters; usually Thor since both of them have the ability to control the weather. I do think this would be a good fight and can even see her winning in some cases, but I'd appreciate it if I don't have to see duplicates of threads that were created 12 hours ago. 
So just to make things clear, this wasn't a hate thread since these are some of my favorite characters. If you got triggered by this, I take no responsibility :P
Someone also told me to include Goku on this thread but I'm not qualified enough to write about him :/
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