Twins Swapping Confessional
Alan and Arthur are twins who are about to marry twins, Beatrice and Bonnie.
The night before the wedding, Beatrice takes her fiance Alan aside and tells him that she has a confession to make - one night, she dressed like Bonnie and snuck in and gave Arthur a blow job. Alan laughs, because he confesses that one afternoon when Arthur was stuck at work, Arthur sent Alan over to satisfy Bonnie's sexual demands, being afraid she might otherwise look elsewhere. Beatrice is of course curious just what Alan and Bonnie did, so the reader gets that detail, plus Alan and Beatrice's make up sex.
Meanwhile, Arthur is telling Bonnie that on prom night, he and Alan switched keys to their motel rooms, and got a taste of each others twin. bonnie laughs, because she and Beatrice did the same thing- so each actually ended up with their own date! They then discuss how surprised they are that they did things thinking they were swapping, even though they weren't. Bonnie then points out that they still owe each other the swap. so Arthur confesses about his swapping places with Alan. Bonnie, not knowing about Beatrice having blown Arthur (he doesn't know it was her either), insists that Arthur needs a shot with her sister...