Here is what happend once:

im on a roleplaying site called Warrior Cats RPG, a roleplaying site. One day , i was looking for a roleplay thread to do with horror and i saw this ! -----> " A Michael Myers Love Story ".

Me: why....just why...ISNT ANYTHING SACRED ANYMORE.

I'm not sure if this would be late or not, but what really aggravates and saddens me is when a terrible RPer is an obvious Mary-Sue tries to guilt-trip you (when you're RPing a Canon character) to have their and your characters in a romantic relationships. Or, have you encountered this before; a horribly portrayed CANON character obsessed with your OC, and also trips to guilt-trip both you and your character....because, I have encountered both accounts of this. (Does a terribly portrayed Canon character drooling over your OC when you don't even want it count?)

Once, I was RPing a Papua New Guinea character I have for Hetalia. I spent quite some time researching him (now a "her", reasons explained later), so I decided he'd go about in traditional apparel; a goatskin loincloth with a sash of dried grass. Here, we have this sex-obsessed Greece RPer who, for whatever reason, does nothing but sleep, attack other character for no legit reason, and fucks anything that walks (excuse my language, but that was it!). My PNG comes walking in, and then suddenly what horrified me was that Greece was the first character to spot PNG, and of course got instantly horny (even though they never met before EVER. Did I mention this was a Neko!Greece, which made things worse....).

He called my PNG over, which got me even more hyped up. He commented that PNG's clothes were "interesting", which confused PNG and offended me. How does someone sexualize a national costume!? That's so wrong on so many levels! She needed to show some damn respect! Then, of course, Greece starts making inappropriate comments, so he (PNG) goes off to flee, no longer comfortable. Greece gets upset (?) and goes off to deliberately break his arm (knowing PNG is an expert in traditional medicine). Of course, PNG couldn't say no, so he healed Greece, only to have Greece to admit his "exquisitely powerful love" to PNG (they had known each other for, what, fifteen minutes....?). PNG says he must refuse for two reasons; first, he was heterosexual, anyway, and gay relationships were looked down negatively in his country. Second, he was still under British rule, so it might anger England and/or the rest of the UK or something. The RPer claims "Greece's heart shattered into a million pieces" (they had known each other for only fifteen effing minutes!), so that when I pointed out this was a bit, you know, rushed? The RPer claims "well, in Romeo and Juliet, they fell in love in seconds!" I replied that that was Shakespeare, this isn't the sixteenth century or whatever anymore! The RPer seemed to chuckle it off (....?) and moved on, but still prays after my PNG. I grew afraid, so eventually I decided to make my PNG a girl instead with hopes to prevent assault from a random yaoi fangirl again. -.-

In another case, involving a Mary-Sue OC obsessed with a Canon character;

I loved to roleplay Holy Roman Empire, and in that room I roleplayed him as a teenager (around 14-15 physically). This Berlin OC comes in, who of course has a ridiculous outfit, is good at EVERYTHING involving arts and the craft, an /amazing/ singer, is effortlessly beautiful, and seems to hate other girls (....?) strides in. I usually ignored her, until HRE and a fem!Austria were having some black tea, which I had the headcanon was HRE's favorite drink. Oh! Then, suddenly, it's Berlin's favorite drink as well! She comes over and helps herself and engages in a conversation with HRE and won't. SHUT. UP. (HRE, at the time, was already in a committed relationships with a fem!Italy).

HRE gets uncomfortable, until his cousin (my Franconia OC, who was already present at the time) joins in the gathering for tea and notices this. During the Middle Ages, Franconia was HRE's personal body guard, so of course she warned Berlin that even though she may be an Imperial city, she better watch it. Berlin, who was getting too chummy with HRE for his own comfort, got up in Franconia's face and was shouting at her (it was a gentle warning Franconia gave, anyway! She wasn't threatening to kill her, or something!) and brought out a horrible German accent, trying to "sound more German". So Franconia, being a bit snarky as she is, starts laughing at her attempt to "sound more German" (they all had German accents, anyway, even if we were drastically typing it out like she was!), then Berlin SNAPS. She starts blaring insults at Franconia's family, regardless that HRE was also a member of Franconia's family. HRE stands up to stop then fight, then in tears Berlin claims "neinbody knows zat she had her heart broken 31-37 times!" She then pronounced her "liebe" to HRE, then HRE finally has to point out some things. First, he was of noble blood and a legitimate child, while Berlin was born after a "drunken incident between Prussia and fem!Germany", thus making her a bastard, so they couldn't be together even if they wanted to. Second, HRE displayed his courtship pendant given to him from fem!Italy and explained he was already courting her. Berlin runs off in tears, but also still lusts after HRE as well. I just never go to that room again.

Those are only two of many stories I have to tell, but basically these have been my worst encounters so far....

Yuugiou... OC's EVERYWHERE. Of course all OC's are female and fall in love with the most popular canon boys. Geez, I can't stand these CanonxOC pairings. I hate them. I love OCxOC and CanonxCanon though.

Treasure Planet! The Disney Film! Is arruined for two Mary Sues!! ToT

MLP, Sonic the hedgehog, Kingdom Hearts...

I'm neutral with OCs, but it gets annoying when they dominate the fandom where it's almost rare to find actual fan art.

What I really hate it how people make OCs, pair them with their favorite character and call it their OTP. It's pretty silly.