Here are some of the better ones that my friends have used.

—— 

"Oh, refridgerators." - Althie, the queen of sarcasm.

"That darn cheeto puff!" - Lizzie, the purest human being alive.

"What the fridge?!" - Althie again. She's fond of this one.

"FIDDLESTICKS!" - Bridget

"She's seriously such a bi— bisicuit." - Caleb, because a teacher walked by.

"Shut up David, you absolute bludger!" - Owen, backstage during theater when Daniel was walking too loudldy or something. I really like this one, actually, I may use it sometime.

"Oh, Hufflepuff!" - Em, one of our friend group's Potterheads

"You abandoned us, muggle!" - Em, when Althie ditched us at Starbucks

"Rapscallion!" - Often in use by Charlotte and Em

"Holy Hamilton!" - Julie, an extreme Hamilfan

"Holy Hephaestus!" - Alex

"Eheu!" - Everyone! It's Latin for 'oh dear' and super fun to say. (Pronounced eh-hew.)

"You're such a caudex." - Charlotte and Alex. More Latin, it means 'blockhead'.

"Oh, persnickets." - Andrew, with this made-up-word.

"Fudge." - Everyone, of course. 

"Shut up, you meeple." - More Andrew and another made-up word.

"Go away, peasants!" - Bridget, Teah, and Grace

"Cheese and crackers!" Is one of my favourites! Also I constantly say things British grandmas would. It's a normal hourly thing to hear me say "oh dearie me" or "oh my heavens!" xD

My friends and I say "go to Tartarus!" quite frequently, and we also use 'biscuit!' as a replacement for some not-as-nice words. Or, in a movie, if someone curses, we yell "biscuit!".

Also, one time, my AE, Sweet Tea, said "Oh, my sugar packets!" which I occasionally use in real life.  

QE and I came up with some fun words. "Oh dashboards." "What the shumu." Etc. I actually used "Oh dashboards" when me and some friends were filming once. For those who watch The Corn Crew, I was with our camera-man and his sister. They just shrugged it off without looking surprised (they've been used to my craziness), but later I heard him ask my brother..."so, what's the story behind 'Oh dashboards?'" "Oh, that? You don't want to know." 

I remember someone once posted saying Shittake Mushrooms, but I don't think that's really fair to the Admins because they know it's a swearword but there's nothing sinister about mushrooms, is there?...so I don't think it should be commonly used.

But I love fandom swearwords! Even though I don't swear very much in real life--I didn't go to school ever, so I wasn't influenced by that....

Merlin's pants.  

...Cho used to say oh my Gandalf...a lot....

My choir teacher uses "Oh foot!" and "Oh my stars." My friend will occasionally say "Holy crabs." and I've taken to saying 'Schist', yes, like the rock. And this isn't really a swear but we say 'Murder blue' when talking about a specific shade of blue and it's just funny because no-one else gets it.

My friends say "cats!" a lot. I also use:

Frigg

Frigga

Oh my Gandalf

*makes weird duck/fart noise*

Bananas

*whispers in awe* Holy TARDIS of Gallifrey...

Van Dyke

Oh my Claaws

Aw schnitzel!

Soysauce

You little prat 

You little Meerkat!*

You little duck!

Youl little Meerduck! 

You little Meerduck dipped in soysauce!

*Meerkat actually is an acronym that stands for Merciless Evil Extermination Racist Killer Assault Terrorists.  

I can give you the backstory to how any of these were invented, if you want to know.  

Oh my gandalf- everyone 

Fudgemstucks...I seriously don't know where that came from.

Merlins beard- again, everyone

Minkle- ummmm...

Jackson: "Confess!  Confess your love to him!!" *runs away*

Sodea: *blushes*

Me: *blushes, then runs after Jackson* "GET BSCK HERE, YOU NOSKCAJ!  I'll KILL YOU!!"

Sodea: "What just happened?" 

Shiaiaisht

Frik

Daaaaing

Sheeioot 

Elena sayd aimt.  You aim at the T? 

Here are some me and my friends say;

-Crapturds!

-Holy Tie-Dyed Llamas Dancng In Bowler hats!

-Chognozzle! (I'm pretty sure chog is made up)

-Oh Corgies!

-Ooh, why I oughta slug you