Given the situation, you showed a lot of restraint. She slandered your mother for God’s sake! Many people would need a lifetime’s worth of cumulative self-control to keep them from at least threatening that right-wing shrew with bodily harm.
Fundamentally the problem in the US isn’t necessarily Christians per-se, but the subset of them who think that “the US was founded as a Christian nation”, and as a result, Christians should get special/preferential treatment, primacy of place, public acknowledgement, and so forth.
And FWIW, I once had someone get mad at me because I wasn’t properly helpful at a Target, and I didn’t even work for Target or at that store. I just had the misfortune to have worn a tucked-in red polo shirt and khaki pants that particular day, and apparently looked junior-managerial. She got even more irritated when I tried to explain, as if somehow I was trying to dodge my managerial responsibilities. In fact, I was an IT guy at a nearby healthcare company and was running an errand during my lunch hour! Some people just get their minds set, and nothing will change them.
Apparently I give off vibes that say “I’m hard at work here, I used to be a Boy Scout, and I know where everything is.” And saying you don’t work there never seems to compute; it’s like they’re so desperate to hear ‘Left-Handed Widgets are in Aisle Seven’ that nothing else is getting past their filters.
I’m usually in a hurry, so I’ll wave in the general direction and say "Head that way and look for a sign that says Plumbing, or someone who works here."
Then I make a quick exit because I hate those dragged-out arguments like the OP, but I’ve heard more than one :hrrrumph: as I’m leaving. Which I imagine translates as "I have been deferred to by people of your class all my life, and I can’t believe you’re not stopping everything and escorting me to the exact product I need, so that my life will continue to go smoothly (rolling along on the backs of the lower middle class).
People like the one the OP interacted with are why I’ve moved over the years from being a quiet, soft atheist to being an in-your-face, hard atheist.
I see a lot of these “brand” guys at my market, and I know not to ask them about anything but their brands. It’s kinda obvious, really. And it’s rare that there’s an actual store employee they can ask nearby. I still blame that awful woman.
When I was till driving for a beverage distributor, I’ve been mistaken for a Target employees while wearing a various shades of blue uniform.
Customers are dumb fucking stupid.
If I’d encountered the “brand” stockers in my local grocery store, the way they work, the only thing I would’ve said is, DO YOU MIND MOVING YOUR @&$%^ STUFF SO THIS SHOPPER CAN ACTUALLY MAKE IT DOWN THE AISLE? 
The problem is the majority of “Good Christians” that stand by passively and let that minority of hard liners pass restrictive laws while, at best, mewling “They don’t speak for the rest of us!”. If the supposed vast majority can’t take the mic from supposed tiny minority and put a halt to their antics then, yes, they fucking speak for you.
I’ve had people on the street, I mean literally on a sidewalk on the streets of Seattle out of nowhere stop me to ask for help with their smart phone or something along those lines. I am a random person with no uniform or anything, just walking along the side of the road, and you stop me for IT help?
Granted, I am an IT professional and I’m able to help them. But how the fuck do they know that?!
I even once had a panhandler ask me if I was in IT. I asked him how he knew that, and he said I just looked like the type. Apparently, he used to be a UNIX administrator. And now he was sitting outside of a convenience store in Pioneer Square asking folks for change. I’m glad I stuck to desktop support.
You deserve a medal for not immediately resetting their phone to factory default settings. If some dork handed a complete stranger their phone they rather deserve whatever outcome they get.
I swear I’m about ready to start carrying a small squirt bottle around to handle these fucking belligerent morons that seem to be flooding the streets. Thing about squirting water in their face is it completely discombobulates them and interrupts whatever interior script they’re following. It doesn’t hurt them a bit but you’d be surprised at how well it works. I have a 75 lb water crazy dog who is nonetheless mightily in fear of the squirt bottle. Works a treat. Works on humans, too, I have empirical evidence.
Do you say “Down, boy! Bad dog!” as you’re squirting someone.
I definitely would, and would enjoy it so much I’d soon start using on anyone who asks the time…
I think i would adopt the Will Smith approach, ie :-
"Keep. My. Mom’s. Name. Out. of. Your. F***ing. Mouth."
I don’t think g-d needs any help slandering anybody. 
Honestly, I’m betting He was far from her mind when she started her tirade.
That makes me immediately apologize and leave the guy to get his job done.
“Hey lady, keep me out of this. I have nothing to do with the bullshit you’re laying on this guy.”
I’m imagining the Joker’s acid flower tucked into his front pocket.
“Excuse me, ma’am, can you help me–”
“SMELL MY FLOWER!”
~Max
I knew I made the right choice to focus on DOS.
WTF are you talking about? I was just describing the mindset that gives you people like in the OP’s story, not the political problems of fundamentalist Christians voting as a block, which is typically not done by other denominations.
Christians of liberal or just non-political denominations have no more power to control these rabid pseudoo-Christians than you do. All we can do is show up, march, write letters, wave signs, and support good people for office, just like everyone else.
I do feel strongly that Christianity is the least of the things that motivate them.
By that logic, Republicans speak for you. 
~Max