They can no more prove the nonexistence of God than we can prove the existence of Him.
Therefore atheism is based on faith that we know enough to say conclusively there is nothing we don’t know, that can be considered “God.”
Faith is evidence of what we cannot see. If we could prove it we wouldn’t need faith.
They are angry because at some point they must face a cognitive dissonance. I tell them that the only honest atheist is one who leaves a little room for agnosticism. Not that God is like the God I’m describing necessarily, but something he’s claiming doesn’t exist.
You can challenge him to whether anybody would have guessed we could have a thousand conversations flying through our heads and with a little gadget (and sometimes teeth fillings when near antennas) we can tune in and listen to any one of them to the exclusion of the others. But then Marconi invented radio and now it’s taken for granted.
Or how about whether relativity existed in a world where Newtonian physics was TRVTH? Until Einstein, it was unheard of for any respected scientist to think they weren’t perfect and complete in all cases, include “extreme” ones that relativity and quantum physics have discovered do not play by the same rules.
They must get angry because their arguments don’t hold up. I give them credit that I cannot prove objectively there is a sentient God, and they can say what they want about how presumptive I am concerning what I think is salient evidence because it’s ultimately based on faith.
So the belief that there is no God, without any doubt, is itself a faith-based claim. So they are just as “religious” about sticking to unprovable claims as I am.
If they want to discuss point, counterpoint, fine. But if they want to get ugly I will have to get amused and console them, maybe even condescendingly.
Let them taste of their own medicine – their arguments are so weak I can play on their turf (and invoke scientific evidence) and still beat them on their home court in front of their friends. They have itty bitty minds with itty bitty ideas and their anger protects those ideas from being challenged beyond their fragile mental comfort zone.