Okay, I'll bite.Stump an atheist. Ask him why he wants proof that God/Jesus exists.
How about "I want proof that God/Jesus exists so that I can examine this 'proof' and determine it's validity."
Actually, it doesn't have to be that complicated. Present me irrefutable evidence of ghosts, spirits, demons, souls, an afterlife, telekinesis, mind reading, levitation, remote sensing, precognition, water witching or reliable predictions based upon the examination of spilled goat intestines and I will cede you the possibility. Whether such beings are worthy of our admiration is another matter altogether. Whatever might pass as improvements to the Human Condition have been brought about by our own efforts.