Normally I only post about rudeness I've personally observed, but this one was just too ripe not to publish.
Sarah and a group of co-workers went out after work to an elegant restaurant. At a neighboring table, a man quietly sat alone. He ordered a dessert, which came with a burning candle. One of the women, upon seeing this, drunkenly declared that "We need to sing Happy Birthday to him!" His mouth full, the man held up his hands in protest, but the drunk ignored him. He had to interrupt the song with pleas for them to stop.
He showed them the picture on his table. It was a photo of his dead wife. It was her birthday, he explained. She was recently killed in a traffic accident.
"THEN LET'S SING TO HER!" the unflappable drunk squealed. And then, over his protests, she boisterously sang to the dead wife, butchering her name.
Nested rudeness: when the man ruefully said that his wife's death was the reason for a new local traffic light, another member of the party felt compelled to point out that "See? Some good comes out of everything."