Disclaimer: Buffy belongs to Joss Whedon and Supernatural belongs to Eric Kripke
Spoilers: Post "Chosen"
It started off innocent.
That was her story and she was stickin' to it.
And that's because it was true.
She was looking for Sam so she could give him some information.
Harmless mission, right?
One would think.
The information wasn't anything important, just more paperwork for Sam to push around, but he wasn't complaining. He was all for fighting the forces of evil, but only when he had to. He preferred staying back at the Council, doing things behind the scenes.
No one complained since the performance of the slayers were at record highs when it came to demonology research and such. All Sam had to do was ask them nicely and maybe give them a nice smile and the girls would quickly act to do it.
Him already being in a relationship didn't matter to the slayers.
"Sam?" Buffy knocked on his door.
"One minute," he replied through the door.
For the rest of her life, until she died again, Buffy would deny what happened next. Somehow, she mistook "one minute" for "come in." Some slayer hearing she had, but of course, she would deny it ever failing her if anyone asked.
Pushing the door open, Buffy came face to face with Sam, who froze at her sudden appearance.
"Don't yell at me, Andrew, I didn't know your boyfriend would be all nakey!"
I take it you weren't expecting that particular ending?