Barney: [laughs hysterically]
Ted: Why? Just why?
Barney: You don't remember?
[flashback to one year earlier:]
Barney: I'll bet anyone ten bucks I can get Ted to grow a mustache.
Ted: Uh... okay.
[present:]
Ted: You sabotaged my next to last chance with Stella for ten dollars?
Barney: [laughing] I know. I would've done it for free. [seriously] But, no. You owe me ten bucks.