Lily (Alyson Hannigan): There's a girl in there.
Ted (Josh Radnor): I know.
Marshall (Jason Segel): And a pineapple.
Ted: I know.
Lily: Who is she?
Ted: I don't know.
In the episode of How I Met Your Mother that first aired on this night in 2005 — "The Pineapple Incident" — Barney (Neil Patrick Harris) was chastising Ted (Josh Radnor) for overthinking things. He kept urging Ted to go with the flow and not think so much, and Barney coerced him into drinking five shots (the bartender's special creation, five blood–red drinks dubbed "Red Dragons").
Ted drank the shots, insisting that they could not affect his brain, but then he apparently passed out. His next memory was waking up the next morning with a sprained ankle, a pineapple on his bedside table and an unfamiliar girl in his bed.
And no one — not Ted, not Barney, not Lily (Alyson Hannigan), not Marshall (Jason Segel) — knew anything about any of those things.
Ted also had a phone number written on his arm. No one had any idea whose number it was.
So he called the number. Turned out it was Carl the bartender's number. He had sent Ted home the night before and had written his number on Ted's arm, telling him that if he passed out in a gutter somewhere, someone should call Carl, and he would come get Ted and take him home.
So that solved that mystery.
But there were still the matters of the ankle, the girl and the pineapple.
By a kind of twisted process of elimination, Ted concluded that the girl sleeping in his bed was Robin. He hadn't seen her face because she was laying on her stomach, but Ted had been calling Robin over and over after drinking the shots, and he figured it had to be Robin.
"Are we dating now?" he wondered, adding that he hadn't imagined things going that way, but perhaps it was necessary for the two of them to become a couple.
Lily told him to go in the bedroom and talk to her, which is what he did.
But just as he was about to wake her up, Ted's phone rang. He answered it, and it was Robin (Cobie Smulders), who wanted to come over to talk about all of Ted's drunken phone calls the night before. Obviously, the girl in his bed was not Robin after all.
Ted returned to the living room and, as they were all wondering who the girl in Ted's bedroom could be, the girl walked through the door and announced that her name was Trudy.
Trudy (Danica McKellar) proceeded to fill them in on what had happened.
During one of his many drunken phone calls to Robin, Ted had been serenading the bar patrons and fell, injuring his ankle. He later followed Trudy into the rest room, believing he was going to be sick. But he wasn't and, instead, got into a conversation with Trudy, who had just broken up with her boyfriend. And, as these things sometimes work out, the two of them wound up back at Ted's place.
Well, Trudy slipped away somehow, and Ted never got in touch with her again. He left messages on her cell phone, but she never replied. And the gang never found out about that pineapple, either. But it was delicious.
I guess some things are destined to remain mysteries.