Ron being rude was the reason Hermione was in the bathroom when the troll attacked the school. 🙄

"Oh, well done!" cried Professor Flitwick, clapping. "Everyone see here, Miss Granger's done it!"

Ron was in a very bad mood by the end of the class.

"It's no wonder no one can stand her," he said to Harry as they pushed their way into the crowded corridor, "she's a nightmare, honestly."
Someone knocked into Harry as they hurried past him. It was Hermione. Harry caught a glimpse of her face -- and was startled to see that she was in tears.

"I think she heard you. "

"So?" said Ron, but he looked a bit uncomfortable. "She must've noticed she's got no friends. "

Hermione didn't turn up for the next class and wasn't seen all afternoon. On their way down to the Great Hall for the Halloween feast, Harry and Ron overheard Parvati Patil telling her friend Lavender that Hermione was crying in the girls' bathroom and wanted to be left alone. Ron looked still more awkward at this, but a moment later they had entered the Great Hall, where the Halloween decorations put Hermione out of their minds.

https://www.youtube.com/watch?v=1P7HQiRceas