There's nothing quite like the joy of making company ever-so-slightly uneasy, and these deceptive chairs with a faux-slant would probably do the trick.
This chair by designer Rasmus B. Fex is called 9,5° and I'll bet you can figure out exactly why. Despite the fact that all the chairs vertical pieces are skewed just slightly, the chair itself — as far as any potential sitter would be concerned — is perfectly level. Despite how it may look, this chair is actually quite sturdy due to the stablizing triangle that sort of jacks the actual seat part up to a normal zero-degree tilt.
As simple as the premise may seem, you probably shouldn't try to make your own out of that rickety chair that's been sitting in your basement. Unless you like sitting on the floor surrounded by splintered wood. [B°Fex via Dezeen]