No Tomorrow - S3-E12
Corrected entry: In this episode Marshall and Lily buy an apartment that turns out to be crooked. When Marshall is hanging the picture it slants to the left of the camera each time he tries to straighten it, however the apartment is slanted to the right, on camera, and also demonstrated by Robin when she rolls the champagne bottle.
Correction: There is no mistake in that scene. The picture tips the correct way for the laws of physics.
Actually the picture shouldn't tip at all, since only the floor is crooked.
Actually you can see that the corners of the wall are perpendicular to the floor so there should be a tip.