A simple childproof cap can easily be converted to an everyone proof cap...
Most childproof caps are made in two pieces. The outer cap will have some sort of permanent cam type flanges and the inner cap will have the locking mating surfaces.
We will be modifying the inner cap on this one...
Step 1: Remove Inner Cap
The inner cap will have to be removed and modified.
The inner cap will pry out with moderate pressure and small force using a flat screwdriver wedged between the outer and inner caps.
Take care not to damage the outer cap as this will defeat the the subterfuge...
Step 2: Modify Cap
Cut the tabs (flanges) off of the inner cap. This will prevent the cap from locking with the outer cap.
Once the tabs are removed, Press the inner cap back into the outer cap.
Step 3: Place and Enjoy
Press, squeeze and tighten the cap onto the original bottle. This will create an almost permanent seal.
Only the most dedicated and determined people will be able to open the now everyone proof bottle.
To get to the contents you can try using excessive downward force on the cap, failing that you may have to pry the outer cap off with a screwdriver in order to remove the inner cap from the bottle.