Being passed up for an internal promotion that you've been preparing for and waiting for for years is always going to sting and make you reconsider your employment—but being asked to train the person they've externally hired over you will definitely grind enough salt in the wound that it will drive you to quit. That's what happened when this employee was passed over for a senior role at their company and asked to train their boss-to-be. They shared their story in a short thread that they posted…