Hey, I got one of those, too!
I can’t remember the exact terms I used but I once explained a major power grid outage to my CEO as something like “chance encounter of human error, one man-made force and two natural forces”.
The statement was just enough off center that it would have been very unusual for someone else to describe it that way.
Days later my exact statement word for word was all over the news feeds.
Krav Manga, I see what you did there.
For myself, it wasn’t actually plagiarism because it was properly sourced, but Randal Munroe once used a piece of information that traced back to me in one of his “What If” columns.
Many years ago, I was reading an article in an obscure scholarly journal, and discovered that the authors had plagiarized a couple of sentences from an article I had written for an even more obscure anthology. I found this mildly annoying, but wasn’t pissed enough to do anything about it.
It turned out later that I had made a minor factual error in those plagiarized sentences. Someone wrote to the obscure journal, taking the authors to task for their mistake. Since they obviously couldn’t say “It’s not our fault, because we stole that part from this Erysichthon guy,” they had to own up to the error and apologize for it. So that worked out pretty well for me. 
It’s been so long that I don’t recall. There were at least two from among my stories that appeared in Aboriginal SF, so I think they were “Screams Are Not Enough” and “Sundials.”
Just thought of another. I put the story of my grandfather and Albert Einstein on my web page. People have referred to it properly, but I discovered some middle school English textbook had taken the story and used it for a reading comprehension exercise (they even put my name in place of my grandfather’s).
I actually was one asked by a Physics magazine to reprint the story. I asked what rights they wanted. They wanted all rights – and said they couldn’t pay me because they were a small magazine that didn’t have the budget. I looked it up and saw they charged $300 a year for subscriptions. And they sold reprints of their articles.
I told them I’d license the rights to them for a payment and a portion of the reprint fees. Never heard from them again.
A joke I made up appeared in Doonesbury!
“What’s the difference between Rush Limbaugh and the Hindenburg?
One is a flaming Nazi gasbag…and the other is just a dirigible.”
I sent that joke to the editor of the Flush Rush Quarterly, who published it, and (I think) that’s how Garry Trudeau learned of it.
As a kid, I came up with the idea for Alex Mack (odd mutated teenager show) months before Nickelodeon started advertising it. I also came up with the idea of adding modems to video game machines so you could play two player from a distance, though, technically, that already existed in Japan. But I didn’t know.
I also remember coining the word “somersault” for a sitting front roll, before learning that was actually what it was called. I wonder though if my little brain made the connection before then.
Obviously none of these were actual rippoffs, but I did for a while think the Alex Mack one was. I told my idea to this old man at Walmart.
When I was in 5th grade I had a book idea of a secret war between vampires and werewolves.
My idea was to have it be one of those two-sided books that would tell the same story of the war (really the buildup to one giant battle) from each perspective.
About a year or two later Underworld came out.
Coincidence? Absolutely!
Wrote a patch for Medieval Total War 2 (which was a horrible mess on release), originally for myself but uploaded it on a fan forum for other blokes to enjoy while waiting for an official one.
I was surprised to find my own code (complete with humorous comments) included in an official patch a couple weeks later.
Yes, it’s true. I am Krav Manga’s evil twin. 
Not exactly plagiarized, but once in the late 1990s, I made a comment in a usenet fan group for a certain celebrity who was having legal troubles. Later, a reporter from the Associated Press e-mailed me wanting my phone number so that he could call me and interview me about it. I found it really weird that he would want to do that, given that I was just Some Random Guy stating an opinion on the internet and had no informed, inside perspective to give. I didn’t even bother replying to the e-mail.
A few days later I’m reading an AP article on said celebrity in my local newspaper and come across a passage that seemed oddly familiar. Only to realize that I was being quoted (by name) from my usenet post, as if it had any relevance to the article (or the legal trouble) at all.
Not plagiarism, just coming up with the same jokes at different times. I once made an online comic with a joke about Dick Cheney being stuck in a Dunk Tank to raise money for the NWO, and about a year later, The Onion did a similar bit.
Later I did a bit about how the Super Bowl game was actually the Superb Owl game, which I discovered much later is a pretty common joke.
When I was 3 or 4 (in 1985 or '86), I came up with the following joke:
“Bert: ‘I’m going to the ice cream store, Ernie, want anything?’
Ernie: ‘Sherbert’”
I’ve recently started seeing it used in memes across the internet, but I’ve yet to see a citation for its use from before 1985, so I’m going will continue to claim that everyone stole my toddler IP.
I got news for you: Publishing a story as a serial and then later releasing it as a single volume goes back to at least the Victorian era. Arthur Conan Doyle, for example, initially published the Sherlock Holmes stories in The Strand Magazine. The short stories were, of course, compiled together into single books. But longer novels like The Hound of the Baskervilles were also released chapter by chapter in the magazine and only later put together in book form.
Tony Millionaire did a Maakies cartoon inspired by an email I sent him. I’ll link if I can find it.
I constantly recycle a Hunter S. Thompson quote (“Writing is like fucking. Fun until you get paid for it”) to fit various situations. Not always with attribution.
Oh, I’m not surprised. I didn’t think the idea of a serialized novel was a new innovation, by any means. I mean, it happened all the time in pulp novels and magazines, right? It was kind of a new thing in comic books, though. Prior to that time, stories had either been self-contained in an issue, or else endlessly serialized like a soap opera. The idea of the somewhat limited story arc routinely being gathered into a trade paperback was something of a new concept for comics at the time. I have no idea where Stephen King got the idea to serialize The Green Mile, it just struck me as odd that I had mentioned the idea, specifically referring to him as my hypothetical example, in a paper of which* I knew him to be a reader*, and then only a short time later, he did exactly what I said in my letter that he did not normally do.
What I find equally interesting is that he hasn’t done it since then.
I was in college when boy bands like the Backstreet Boys and NSYNC were popular, and as a joke with some friends made up a boy band style song called “Baby”. About the only word in it was “baby” – it went “Baby, baby, baby, oh baby, baby, baby…”
Unfortunately for me but luckily for Justin Bieber, I never bothered to write this down or record it.
Back in about '90 or '91, Tom Snyder had a ‘call-in’ radio show. So I called in. Constantly. Trolling. One night I called in and just off-the-cuff talked about the “Imminent Alien Invasion of 1992”
A few months later, the “Weekly World News” had an article about the “Imminent Alien Invasion of 1992”, which agreed in all particulars with what I had made up, on the air, live, on Tom Snyder’s radio show.
Yeah. The “Weekly World News” plaigerized me.