threesome with two sisters
Vulgar slang term for a sexual threesome involving two women who are sisters. The word is a play on 姉妹 (sisters) and 丼 (donburi, a bowl of rice with toppings), metaphorically suggesting a 'bowl' containing two sisters.
I saw the word 姉妹丼 on an online forum, but it's a pretty vulgar slang term.
He jokingly said he wanted to 'have a sister bowl' and creeped everyone out.