Ted: MacLaren's Bar, four years ago...
[flashback to MacLaren's four years ago. Ted and Barney are both wearing tuxedos:]
Barney: How do you keep a girl from becoming your girlfriend? Simple, the rules for girls are the same as the rules for gremlins.
Ted: Gremlins?
Barney: Gremlins. Rule number 1, never get them wet. In other words, don't let her take a shower at your place. Number 2, keep them away from sunlight. I.e., don't ever see them during the day. And rule number 3, never feed them after midnight. Meaning she doesn't sleep over and you don't have breakfast with her ever.

Robin: Where do you see this relationship going? My God, that sounds so cheesy.
Barney: I know, right?
Robin: Totally. But hum... Where do you see this relationship going?
Barney: I don't know. I mean, it's not like I don't like you. I just haven't had a girlfriend for a long time. I hope that doesn't make you mad.
Robin: Mad? I feel the same way. I suck at relationships. I mean, except with Ted. Man, he really got it right. I know it's a cliché, but... he really ruined me for other men.
Future Ted: [v.o.] Of course, I wasn't in the room for this conversation, but I have to imagine Robin said something like that.

Future Ted: [v.o.] I still hadn't decided what kind of professor I wanted to be, authoritative or cool guy. I thought I would decide in the moment. And I did. About 20 times.
Ted: Good morning. What's up, dudes? Silence! This is Architecture 101. I am Professor Mosby. But you can call me Ted. Professor Mosby. T-Dawg. Do not call me T-Dawg.
[The blonde woman raises her hand. Ted imagines Barney appearing as a guru.]
Barney: Never take questions on the first day. It shows weakness. Also, don't look right here [points to the woman's breasts] Okay, good luck. Byesies.
Future Ted: [v.o.] This was it, my crossroads moment. What kind of professor was I gonna be. I had to decide.
Ted: Please save all your questions until the end of the lecture. Thank you! Now...
Future Ted: [v.o.] Professor Mosby had arrived. Of course, if I had taken that girl's question... who, by the way, was not your mom. Your mom was sitting... Wait, let me finish this real quick. Here's what that girl would have said.
Blonde Woman: I'm sorry to bother you, Professor Mosby, but this isn't Architecture 101. This is Economics 305. You're in the wrong classroom.
Future Ted: [v.o.] Yes, I was in the wrong classroom. And thus began the most humiliating seven minutes of my life.
Ted: Here's your think-about-it for the day. Every single person in this room... is already an architect.