Rockstar released a patch for this on Jan. 6, 2011. So if you downloaded the content and couldn't get the achievement because it was bugged, you can finally get it now.
As for getting the actual achievement, in a multiplayer poker game (you can do this with as little as 2 people), simply bluff a really crappy hand like maybe a 2 and a 4 and go all-in. Usually the other players will fold. If that doesn't work the first time and everyone goes all-in, try it again a few times and you should get it.