[Coda]

It might be possible to charge something as light as a pen enough that it can hold its own weight electrostatically against a wall. It's certainly possible to do that with an inflated balloon. (Try it! It's fun.)

A general principle in physics, that holds true at all scales, from subatomic to universal, is that processes by default proceed towards lower-energy states or more stable states. (Usually these are equivalent, but there are some cases where a stable state has more energy than an unstable state; the most common examples are endothermic chemical reactions, which absorb heat from the environment to make a final compound that's more stable than the reactants that went into it.) A ball at the top of a hill has more potential energy than a ball at the bottom of a hill, and it doesn't take much of a bump to cause that ball to proceed to a more stable, lower-energy state. To make a system move the other direction, you have to put energy in.

It takes work to separate charges. The greater the difference already is, the more effort it takes to separate them further. You know that like charges repel, so as you get more negative charge gathered on one object, those charges try to push each other (and further negative charge) away. The same is true of positive charge. As you keep forcing charge in, the equilibrium will be such that even the air molecules bouncing off the surface of the object will have an easier time holding that charge than the object itself, so in effect the object bleeds off excess charge into the atmosphere.

And you already know what happens when the potential difference between two surfaces gets too great -- the electrons will actually JUMP from one side to the other through whatever path they can find: sparks and lightning.