Okay, so being that I am that person who burnt their hand on the stove several times as a child before learning my lesson, I still search for RPs on Gaia occasionally and am actually fairly often rewarded with a good RP...
This is not one of those times. I got a PM from someone asking about a Harry Potter male/male RP with OCs, the person didn't capitalize a single letter, however some people do save their grammar and punctuation skills for the RP, so I gave her the benefit of the doubt and agreed. Then she asked if she could be a cross dressing MTF character. I said no because no one I've ever RPed with does it right and use it as another lolionlyplayukegaiz ploy which is annoying. She agreed not to play that type, however what she came up with instead was worse. The opener she sent was incoherent roundabout babbling about nothing in particular, was only a paragraph and was mostly the character's appearance and implausible backstory. Basically it amounted to her character being the son of a mudblood squib(which she spelled 'squid') and a muggle but he was Salazar Slytherin's ancestor. Um...What? How? Newsflash, ancestors of Salazar Slytherin are Marvolo, Morfin, Merope and Voldy-pants. Marvolo's dead, Morfin's mad and dead, Merope is dead and only had one child, Tom Riddle, who CANNOT REPRODUCE BECAUSE HE'S DEAD, IF YOU WERE VOLDEMORT'S CHILD AND YOUNGER THAN HARRY BY ONLY A YEAR, THAT IS COMPLETELY IMPLAUSIBLE. The rest of the babble was incomprehensible, but I will not be sticking with this RP at all, I fully intend on replying that I just cannot deal with that level of fail not to mention I was given nothing to work with, just stuff it would be impossible for my character to know like his inner thoughts and feelings and also his lineage. My character is a fifth year and therefore doesn't know legilimency, so how am I supposed to respond to that at all and what would compel me to come sit next to someone who all my character would know about him is that he's a filthy mudblood when my character is a Draco wannabe?
TL;DR: Implausible Mary Sue gives me nothing to work with and expects a response.
EDIT: Also another annoyance, when people obviously didn't read the rules and then get all indignant and call the person they contacted an asshole or somesuch just because the little shit who responded didn't read the rules, didn't read the pairings or the plots and came up with something completely idiotic.