Effect:
Stack three glasses on top of each other.

Solution:
Place the first glass on the bar. Imagine that if you look down on top of it that it is the face of a clock. Place the second glass at 10 o'clock and the third glass on top of the second at 2 o'clock. As with every trick, you should practice this alone before you try in front of anyone. No need to look any more foolish.