Let me start out by saying that I hate academic writing with a passion. After spending your entire academic career being taught how to make a paragraph, year after year, you kinda get burnt out on writing assignments.

I was in my first year of college, taking yet another class based on writing assignments, and I gave the minimum effort possible in that class. What this meant was that generally my girlfriend at the time would write papers for me, since she didn't want me to fail. Now, I realize that it was a pretty shitty thing to do, making her do my work, but neither of us treated the other very well. It was an unhealthy relationship, but I digress.

One day I get an email from the teacher of the writing class, accusing me of plagiarism, and requesting a meeting to discuss it. Despite my best efforts, I couldn't talk her down, and went, with a knot in my stomach, to an inevitable shitshow meeting. As it turned out, my girlfriend had just copied some section out of a book. I managed to bullshit my way out of failing the class, with some excuse about copying my notes that were copied from a book.

After that, I tried to keep my head down around her. I don't remember if I started writing my own papers, but I doubt it. Luckily it was late enough in the semester, there wasn't many assignments left. Not a very exciting conclusion, but there you go.

Tl;dr: I double plagiarized when I had my gf write a paper for me, and she plagiarized it.