This is not MY family story, but one I saved a copy of from somewhere on the web, and remember from reading it several times. I lost the original in a hard drive crash last year, so this is from memory.
The guy who told the story, I think his name was Danny, accidentally got a view of his older sister Wendy one Thanksgiving. She was home from college and was making dessert for Thanksgiving dinner, a chocolate custard. She put the mixture on the stove and went to go take a quick shower. When she got out of the shower, her dad yelled to her that it was boiling over. She wasn't fully dressed yet, so she threw on a robe and ran down to take it off the burner. Stove and counter space was at a premium, so she quickly transferred it into a bowl to make room for other stuff.
Well, the mixture was too hot, and... I can't remember if he said the bowl was a thinner glass or ceramic that actually shattered in her hands from it, or if it was plastic and it melted right through, but somehow the bowl didn't hold up and the custard ended up splashing all over her robe. She yelped loudly from surprise, and, not wanting to get scalded, hastily tore off the robe off herself and discarded it. Her yelling got the attention of both Danny and his father, who soon appeared in the kitchen to see what was happening. Danny said he hadn't really gotten a good look at his sister ever before, but she looked incredible. Underneath the robe, she had on a bright blue thong, and absolutely nothing else.
Once everyone realized what had happened, and that she wasn't in danger, their laughter and her embarrassment set in, and she covered her breasts with her arms and stalked out of the kitchen to get dressed again. Danny teased her about the incident all weekend.