Quote from Barney in Slap Bet
Ted: Meanwhile, Robin tells me nothing.
Barney: Fine, do you want to know what Robin's secret is?
Ted: You know?
Barney: Of course I know. She couldn't look at us. Her face got flushed. That's shame. Our friend, Robin, used to do porn... wait for it... ography.
Ted: Yeah, we didn't really have to wait for that. And it's ridiculous.