I just gently push the primer out with the decapping pin. Never had one go yet, but I keep my hands well out of the way as well as wearing safety glasses. Primers are designed to work with a sudden concentrated application of force. If it were otherwise then they would be going off when you tried to seat them.

The idea of making a primer inert with WD40 is just a myth and has been disproved many times. The main thing you have to realize is that primers are sealed with a lacquer during manufacture. So first thing you have to do is break down this lacquer seal with a solvent like acetone or cellulose thinners. Even then WD 40, which is just a light oil with waxes in dissolved in it, failed to destroy the priming compound.

To be absolutely certain a primer is dead the only way is to fire it off. Then clean the gun as it will leave a lot of highly abrasive residue in the barrel.