This is the Star Trek TNG Ten Forward Door Cover available from ThinkGeek. It's a 38" x 84" piece of printed polyester with elastic corners (like a fitted bed sheet) that fits over a standard interior door to make it look like the entrance to the Ten Forward bar in Star Trek: The Next Generation. And, as you can see in the picture above, it doesn't really deal that well with door handles, so you're probably going to need to cut a hole if you want your friends to take the new entrance to your rumpus room seriously (personally I went with a beaded curtain that glows under blacklight and have zero regrets but tons of trippy swingers parties).
Keep going for a closeup.
Thanks to carey, who wants a door cover that looks like the room inside so people are constantly walking into it for a good laugh.