The toothpick, potato and forks system is in equilibrium in the border of the glass! As well as the circus equilibrists, our system is suspended in the border of the glass without falling. This fact is due to the existence of a virtual point in the toothpick, where the whole mass of the group is "concentrated". When we support that point in the glass border, it is as if we have placed there a virtual object with an equivalent mass.
In the system of the present experiment, the mass gravity center is located in the toothpick because the potato weight is compensated by the forks weight. Thus, when you want to equilibrate yourself, find the intersection of your symmetry axes and move you until you have that point above the place where you want to stay. Try it, but don't hurt yourself!