A short lesson in wax might be in order.
Wax has a poor water resistance. Carnauba is better than most other waxes because it is harder, but it is too hard to use in its natural state, so softer waxes are mixed with it to make it useable. Those are usually beeswax or paraffin, both of which have a poor water resistance, and are easilly damaged by water. Silicone is added to auto waxes so they won't be damaged by water.
Silicones are not used in woodworking waxes because it can cause all sorts of problems with finishing - "fish eye" in lacquer and shellac, poor adhesion with oil and waterborne finishes. Silicones are very invasive in the shop and will transfer to everything we touch if we use it in the shop and are not careful. These problems may often be overstated a bit, but woodworkers choose to not use any automotive waxes in the shop because that is the easiest solution to the problem.
That doesn't mean you cannot use it on a pen. Just be careful with it. Treat it like what it is - a contaminant that can cause you harm. If you don't, you will be back here asking why you are having finishing problems.