My wife of many years has completely lost her sex drive due to anti-anxiety meds.
My brother in law is fat, out of shape, and drunk more often than not.

As a result, (and without their knowledge) my sister-in-law & I spontaneously fooled around once while they were both unconscious. (My wife "happily" asleep, brother-in-law passed out shitfaced) It was undoubtedly one of the best nights of sex I've had in years.

They're staying with us this weekend and although I feel slightly bad about it I'm planning on having lots of vodka and cheep beer available (their respective drinks of choice) in the hopes of recreating the experience.