Here's one theory about the origin from Wikipedia:
The origins are uncertain, but a common theory is that the expression arose after Conservative Prime Minister Robert Gascoyne-Cecil, 3rd Marquess of Salisbury ("Bob") appointed his nephew Arthur Balfour as Chief Secretary for Ireland in 1887, an act of nepotism, which was apparently both surprising and unpopular. Whatever other qualifications Balfour might have had, "Bob's your uncle" was seen as the conclusive one.
Salisbury is widely believed to be the Uncle Bob that the expression refers to. "Bob's your uncle" is said to derive from the supposed nepotism of Lord Salisbury, in appointing a favorite nephew, Arthur Balfour, to several political posts in the 1880s.
"Bob's your uncle" is an exclamation that is used when everything is alright and the simple means of obtaining the successful result is explained.
Here in America, we'd say, "a piece of cake" or "easy as pie." But I rather prefer, "And Bob's your uncle."
Today's episode was prompted by something that happened one year ago. I recorded the event on my personal Facebook page. Here's what I wrote.
Grandson #3 (Easton) and grandson #4 (Cason) went with us to see my parents yesterday. On the ride home Easton sees something and the obsession begins. It's the little marking on the side pillars of the car indicating that there's a side curtain airbag.
He's reading out the letters and asking, "What does that say?" All the letters are capitalized though, presenting a new challenge for his reading skills. From the backseat he's announcing the letters. "S, L, D, E, C, U, R, T..." No break or pause, just reading the letters in straight succession. I quickly realize the problem. The L isn't an L. It's a capital "i."
Me: "That doesn't spell anything. S,L,D aren't the first letters to anything."
Easton: "Yes, it is. That's what it says, S, L, D, E, C, U...(he goes on to announce every letter for the umpteenth time)."
Me: "That says, 'Bob's your uncle."
Easton: "No, it doesn't. Bob's your uncle doesn't start with S."
Me: "Sure it does."
Easton: "No, Bob's your uncle doesn't start with S."
Me: "What does 'Bob's your uncle start with?"
Me: "Very good."
Me: "That second letter isn't an L, it's an "i."
Easton: "But it doesn't have a dot."
Me: "It's a capital i. All those letters are capitalized."
Easton: "But it's S, L, D, E..." (again reciting every single letter)
Me: "It says, 'Side Curtain Airbag." (I go on to explain what that is)
Then comes a 10-minute conversation on how those airbags deploy. And I interject "Bob's your uncle" some more along the way.
Me: "When the airbags come out they say, 'Bob's your uncle' on them."
Easton: "But I've never seen them say, 'Bob's your uncle.'"
Me: "Because you've never seen airbags. They don't come out until you crash the car. You never want to see 'Bob's your uncle' unless you crash."
To add confusion, Rhonda inserts, "Cale is YOUR uncle."
Easton: "Then why does it say, 'Bob's your uncle?"
Me: "To let you know the airbags are out. And uncle Cale answers to, 'Bob.'"
This goes on for about 5 more minutes with Easton growing increasingly skeptical. Rhonda finally tells him I'm "pulling his leg." Of course, that means she has to explain what that phrase means.
Easton: "I thought so. I knew it didn't say, 'Bob's your uncle.'"
Now, I'm Googling for Bob's Your Uncle t-shirts in kid's sizes! I'm also coaching him to call Cale "Bob" the next time he sees him!
I smile every time I think of that car ride.
I wish Bob was my uncle, but I do have a cousin named Bob.
Easy peasy. That's our hokey American equivalent. Much less clever than, "And Bob's you're uncle."
That's that. Kinda sorta the same thing.
I don't know if the story is the correct origin of the saying, but I hope so because that makes it funnier to me. Some ner-do-well fella gets a high position and everybody stands around questioning, "Who? Who? Who got it?