Robin: And it's not like the opposite would work. There's no way a guy could pick up a girl, going around talking like a little boy.
Barney: Challenge accepted.
Robin: No.
Barney: I, Barney Stinson, will pick up a girl whilst talking like a little boy.

Barney: No one... I mean no one... could get laid wearing these. [laughs] Challenge accepted. I, Barney Stinson, being of sound mind and amazing body, will wear these overalls until I have sex with a woman. [runs off]
Robin: I actually dated that guy.

[flashback:]
Barney: All right, next challenge.
Lily: Oh, this is an all-night thing? Okay. Um... Pick up a girl wearing a garbage bag.
Barney: I'd be Glad to. Just hope she's not too Hefty. And those are all of the brands of trash bags I can think of.
Lily: I'm not done. You also can't use the letter E.
Barney: Challng accptd!

[flashback:]
Barney: Seriously, guys, you're gonna have to try harder than that.
Robin: Challenge accepted.
[later, at MacLaren's:]
Robin: Excuse me, hi. I'm Ryan Gosling's personal assistant. He saw you as you were walking in, and he sent me over to tell you to wait here. Be cool. This is real. Okay? But listen. Ryan is super shy. I know. Heh-heh. Which means if he comes in here and sees you talking to some other guy, he's gonna turn right around and leave. Nod if you understand.
[back at the apartment:]
Robin: Redhead at the bar.
Barney: Challenge accepted!
[later at MacLaren's:]
Barney: Hey there.
Woman: Get away from me!

[flashback:]
Barney: Please, Ted and Robin are not platonic. Just like me and Robin are not platonic. Just like no two single people in the world are ever platonic. Symposium. Two people are only platonic if in the next 20 minutes, there is no chance of them hooking up. Truth is, I only know of one genuinely platonic relationship.
Lily: You and me.
Barney: Don't make me laugh, Lily. You want to hit this so hard. Seriously, she's playing footsies with me as l... Ow! No, I'm talking about Marshall and Robin. [v.o.] Marshall and Robin wouldn't hook up even if this happened.
[fantasy, Lily runs into MacLaren's with a bomb strapped to her chest as Marshall and Robin talk:]
Lily: Marshall! Robin! If you guys don't full-on make out in the next 20 minutes, they're gonna blow me up and everyone in this bar!
Marshall: Oh, God, no. Anyone but Robin.
Robin: I really don't want to do this.
Lily: Guys, we have no time. Just do it!
[19 minutes later:]
Marshall: I'm sorry, baby. I just... I can't do it.
Lily: Aw...
[back:]
Barney: And the only survivor was me, because I was upstairs banging Ted's mom. What? Get that blond girl's phone number? Challenge accepted.