Now take this same tilting idea, but tilt a group of wall hangings all in the same direction. You can do it only slightly, or increase the angle. Notice in the second frame, the pictures on the right are still nearly straight, but as they move left, the others become increasingly angled. In the third frame they are "spilling" off the wall.
You want to be subtle, but you don't want your guests to miss it. Oftentimes, they will look at the wall, look at their drink, then look at the wall again. Some have even asked if the floor is crooked!
So, after the party, a quick straightening up and your room is back in order. Again, you haven't spent any money and there is nothing to clean up.