Take a gander at Conversational Terrorism, a selection of bon-mot assaults and oratory tricks to siderail a topic. And then don’t do them.
“I would like to answer your question directly, but considering your past reactions / ability to cope with the truth / emotional instability, I feel that to do so would be a disservice to you at this time.” [Other person gets (justifiably) upset.] “See, what did I tell you. You are flying off the handle already!”