Do you think Harry would swear or has sworn? Such a niche question, but trying to realistic write him swearing is such a mixed basket. On the one hand, I don't really picture him doing it, even under extreme distress. But I can also imagine him letting out a light swear if he's having a bad day and has a minor inconvenience
I 100% believe Harry swears. This post ended up being a little longer since I kinda went off and detailed how a bunch of characters in HP swear, not just Harry.
Sometimes, characters are shown to "swear" on page:
âBlimey,â said Ron weakly. (CoS)
âBlimey, it is!â said Ron quietly (OotP)
âWhat in the name of Merlin are you doing?â said Ron (OotP)
âWhy the hell,â panted Ron (DH)
âIâll join you when hell freezes over,â said Neville. (DH)
âMerlinâs beard,â Moody [Barty] whispered (GoF)
âMerlinâs beard,â said Mr. Weasley wonderingly (OotP)
âHarry, what the hellâs going on?â asked Bill (DH)
âBlasted thing,â Snape was saying. (PS)
("Blimey" and "blasted" are here since they were considered mild swear words when they became part of the language like "gosh" and "darn". "Merlin's beard" is kinda like saying "Jesus Christ" which was also considered a mild swear, even if no one really considers most of the above swears by today's standards).
The above is done when the swears are (very) light and something that you could print in a children's book. But sometimes, characters swearing is censored in the books:
Dean swore loudly. (CoS)
Thankfully, Snape sneezed at almost exactly the moment Ron swore. (CoS)
Ron dropped several boxes, swore, and made a rude hand gesture at Fred that was unfortunately spotted by Mrs. Weasley, who had chosen that moment to appear. (HBP)
and Lee swore so badly that Professor McGonagall tried to tug the magical megaphone away from him (PoA)
The lift clattered into view and they hurried inside. Every time it stopped Mr. Weasley cursed furiously and pummelled the number nine button. (OotP)
When that happens, I assume the swears are ones JKR couldn't get away with in a children's/YA book series. Like: "fuck" or "shit".
(Molly calling Bellatrix "bitch" is the only harsher swear word not censored in the books)
When Harry swears, it's sometimes not censored:
âShe doesnât love me,â said Harry at once. âShe doesnât give a damn â â (OotP)
âAnd he didnât think my mother was worth a damn either,â said Harry (HBP)
âWhy not?â asked Harry. âLetâs get rid of the damn thing, itâs been months â â (DH)
âWhere the hell have you been?â Harry shouted. (DH)
But often enough, Harry's cursing is censored:
Harry swore under his breath (OotP)
Harry swore and turned away. (OotP)
Harry swore at the top of his voice, spinning on the spot to see where Mundungus had gone. (HBP)
Harry swore. Someone screamed. (HBP)
So, to me, this suggests Harry says "fuck" or British stuff like "sod off". He 100% does use harsher swears, and it's in character for him to do so. He swears under his breath when shit goes badly or he finds himself in a situation he really doesn't want to be in. He swears loudly when Mandungus escapes him, so when he's really angry, he can go and shout a proper F-bomb. Let Harry say "fuck", his life sucks and he deserves it.
Ron also swears sometimes harsher swears than "hell" or "bloody hell" but he does so more rarely than Harry and when things are really bad. Usually, he goes for lighter stuff like: "Merlin", "hell", or "blimey".
Hermione doesn't swear except for the "Merlin's pants" comment in DH which was clearly meant to be "Merlin's balls" but JKR got censored by her editors and one time she says "damn" in DH. Hermione doesn't even use light swears like "Merlin", "damn" or "hell". She, just, doesn't swear until DH, and even then only twice. Like, her most extreme for the majority of the books is going: "oh my", "oh my god", or "oh my goodness". Hermione is the only member in the Golden Trio that doesn't swear:
âOh, my â â Hermione grabbed Harryâs arm. (PoA)
âOh my goodness,â said Hermione suddenly (PoA)
âOh gosh, I forgot!â said Hermione (OotP)
âOh my ...â Harry heard Hermione squeal, terrified, beside him. (OotP)
âToday?â shrieked Hermione. âToday? But why didnât you â oh my God â you should have said â â (HBP)
âOh my â !â shrieked Hermione, as she and Ron caught up with Harry (DH)
I went a bit off track, but theses are some characters and how they swear that I found while searching this:
Harry, Dean & Lee: swear in profanities that need to be censored ("fuck", "shit", "sodding hell") often and sprinkle lighter swears ("hell", "damn") in there. Harry uses "damn" relatively often.
Ron, the twins, Bill & Arthur: use mostly light swears ("hell", "bloody", "blasted") but use some harsher swears ("fuck", "shit") when needed (and Molly isn't looking).
(I assume Ginny is in this above category too, but I only found her saying "damn" once)
Neville, Dumbledore, Hagrid & Snape (at least, when we see him): use only light swears such as "hell", "blasted" or "Merlin" and its derivatives.
Molly: Doesn't really swear except that one time (calling Bellatrix a bitch).
Hermione & Luna: never use profanities unless really at their limit. Don't even use light swears or "Merlin" and its derivatives. Hermione says: "oh my god" or "oh my goodness", Luna says: "oh, no".
Lupin doesn't swear anywhere on-page either.
Surprisingly I couldn't find any mention of Sirius swearing, not even light stuff (like "Merlin's beard"). I guess he really was raised to have proper manners. Or maybe he's actively censoring himself in front of Harry to be a good rule model.