Bob's your uncle, as I understand it, has two basic meanings: the first is that everything was done in the best way possible. It was done quickly, efficiently and with minimal disturbance around it. The other meaning is that if you follow my directions exactly, you're assured of a good outcome every time. Shaun is talking about a night of sex he had; although the line "Four fall in a bed" leads me to think that this was a foursome and not a threesome. He's using the second meaning of Bob's your uncle: do it this way and you're assured of a good outcome.
Bob's your uncle, as I understand it, has two basic meanings: the first is that everything was done in the best way possible. It was done quickly, efficiently and with minimal disturbance around it. The other meaning is that if you follow my directions exactly, you're assured of a good outcome every time. Shaun is talking about a night of sex he had; although the line "Four fall in a bed" leads me to think that this was a foursome and not a threesome. He's using the second meaning of Bob's your uncle: do it this way and you're assured of a good outcome.