My probable reaction before reading this, now hopefully replaced by the OP if I can remember it:

Mugger: "Give me five dollars, and I'll save 3↑↑↑3 lives using my Matrix Powers."

Me: "Here you-- Wait a minute, I could give these to the MIRI, but I can't do that if I give them to you. There's, like, 1/1 000 000 000 probability you're speaking the truth, and the probability of them making the difference between a negative and positive singularity, wich'd make a difference for way more people like that all over the multiverse, maybe."

Mugger: "... you are terrible at pulling numbers out of your ass. Are you even trying? Unimaginable amounts of lives are on the tine here!"

Me: "I can't deny any of that. Bye!"

me continues never getting around to actually donating and spends the money of something frivolous