"Do I Know You?" is the first episode in the fourth season of the television series How I Met Your Mother and 65th overall. It originally aired on September 22, 2008.
Future Ted tells his children that the longest pause in anyone's life is right after they propose to someone; Present Ted, during this pause, imagines all of Stella's possible responses ("No", "Oh, God no", "I already agreed to marry the quarterback from your high school", etc.), after which Stella gave her actual answer of "Yes". Ted and Stella spend the summer happily engaged; Barney goes through physical therapy; and Marshall copes poorly with unemployment. At McLaren's, Robin expresses discontent with her newscasting job, describing herself as a bogeyman with a teleprompter. In response, Barney laughs too hard at this joke.
The next day, Barney gets Lily to come over to his apartment and confides that he is in love with Robin. She agrees to help him if he will stop having one-night stands with bimbos. He tries to call Robin but panics and leaves a high-pitched gibberish voice mail instead, followed by another awkward, unsuccessful phone call. Lily sets Barney up on a dinner date with Robin, where he behaves quite unlike himself: not taking advantage of opportunities to make sex jokes, ignoring their waitress's generous cleavage, and being interested in the goings-on of Robin's day, especially when she admits her insecurities about possibly applying for a potentially better job at a rival news station. Afterward, Robin gets April (their waitress) to go home with Barney by telling her that he is the second baseman for the New York Yankees. Barney tells April that on any other night, he would try to convince her that he was a Yankee, but he can't because he is in love with the girl who just left. At Barney's apartment, he tells Lily about what happened. Lily is sympathetic until April comes out of Barney's bedroom. He admits that he lied about not hooking up with April but that all the other stuff he said is true. Lily leaves, disappointed. Barney turns on the TV to Metro News 1, affectionately watches a brief segment of Robin's newscast, and goes back into his bedroom with a smile on his face.
Marshall asks Ted for some wedding shower gift ideas for Stella. He asks if Stella likes to cook, what her favorite color is, or if she has any hobbies; Ted doesn't know the answer to any of these questions. It is determined that Ted doesn't know Stella's eye color, so he says they are the color of the ocean after a storm, though he doesn't actually know what color that is. Ted later makes dinner for Stella and uses peanuts as the "secret ingredient", which, unknown to him, Stella is deathly allergic to. After they go to the hospital, Ted and Stella ask each other their "firsts" (first kiss, etc.), and she replies "Dale Harris, 2nd Grade" multiple times. During that dialogue, Ted finds out that Stella has never seen Star Wars, his favorite movie of all time. Marshall is shocked when he learns this, saying that "nobody" hasn't seen Star Wars. They end up watching it and Ted concludes that if Stella dislikes it, he cannot marry her. The next night, Ted and Stella watch Star Wars, but Ted is really watching Stella to gauge her reactions. She mistakes this for foreplay and tries to kiss him, but he rebuffs her with "great scene, great scene". Eventually Stella asks him to leave the room for the time being, so she can watch the movie alone. When it is over, she tells Ted and Marshall she loves it. After an ecstatic Ted leaves, Stella confides to Marshall that she hates it. Marshall is very concerned, but Stella is convinced that she can pretend to love Star Wars for the rest of her life with Ted, to which Marshall gives her his blessing to marry Ted.
Donna Bowman of The A.V. Club rated the episode B+.
Michelle Zoromski of IGN gave the episode 9 out of 10.
Joel Keller of TV Squad graded the episode as mediocre, labelling Stella as the opposite of Dr. Elliot Reid, Sarah Chalke's other TV doctor character in Scrubs. He saw the Barney-Robin story in the episode as "emotionally-satisfying" as Barney struggles with his feelings for Robin and his playboy lifestyle.