(not having seen the episode, from what i gather as discussed here -- basically, barney went from "game player" to just "player" based on a challenge to bed women?
It might be paid product placement from WotC. There was a post a while back from Scott Rouse saying that they did something similar (though more extensive) in Terminator: Sarah Connor Chronicles.
The fact that they actually bothered with minis, a screen, and a d20 suggests it. Or maybe a writer just brought in his own gear.
(not having seen the episode, from what i gather as discussed here -- basically, barney went from "game player" to just "player" based on a challenge to bed women?