I don't remember ever actively rejecting a prayer.If someone was praying to me on my way to a medical facility, I'd probably either reject it politely or have the person arrested for harassment depending on the circumstance.
As an openly gay atheist in a small Christian town, who spends a fair amount of time doing volunteer stuff and going to church, I get prayed for a lot.
I suppose if I thought someone was really trying to puss me off I might, but that's super rare. Possibly because I am nearly as acerbic in real life as I am on RF. Passing me off doesn't usually end well.
Tom