Add a drop of oil to the primer, making sure to get it on the priming mix to render it inert and let it sit awhile. This will deaden it. After decapping thoroughly degrease the primer pocket and interior of the case or your subsequent loads won't go bang.
I've decapped buggered up primers with nary a bang because the primer must be struck a quick, hard blow to detonate it but hesitate to recommend the procedure to anyone else, since it's your eyeballs and not mine.
Better safe than sorry. Not being able to see cuts your shooting career out completely, and we don't want that.
I've had this happen before and just run it through the die. Never had a problem. I have decapped live primers before and never had one go off. I've also put primers in upside down and decapped them with steady pressure and never had them go off. The key is to do it slowly and wear eye protection.