“Is Pepsi OK?”
“No. I will drink water out of the toilet in the restroom.”
"Sorry we don't have Coke is Pepsi fine?" "Actually no it's not..." Do you refuse other brand colas?
I have no preference…
AS LONG AS IT’S PROPERLY CARBONATED!!!
So many restaurants seem to serve soft drinks in principle only. Meaning, it doesn’t matter if it’s flat, warm and poorly mixed. It’s a soda, so be happy with it!
I’ve actually taken to bringing my own to a certain restaurant I frequent because their soda is crap. Good thing I like their food, because they haven’t done anything about the soda despite my many complaints. But they don’t seem to mind me bringing some and losing the drink revenue.
This is me. People who can detect a difference in taste between Coke and Pepsi astonish me. I just don’t notice.
I would often say, “I’ll have the diet version of whichever cola you are affiliated with.” But that’s because I’m a pompous windbag. 
For me, anyway, the difference in taste between Diet Coke and Diet Pepsi is quite noticeable. To me Diet Pepsi has a weird “hint of JP5” flavour to it. It’s not so strong that it’s undrinkable, but I would much rather just drink club soda or something of that nature.
For me switch the last two. I’ll drink DIet Coke but if the option is Diet Pepsi then I’ll take water thank you.
I used to say I’ll just have diet and left it at that. But now some place serve multiple diet sodas. Oh well.
I prefer Coke Zero but will take any diet cola.
All colas taste like malted battery acid to me. But I LIKE malted battery acid, so whatever they have is fine.
I do have preferences. How strongly I insist on them depends on the circumstances.
It’s harder to tell with soda served from a fountain, those can be very inconsistent in the mixture as noted below. The syrup isn’t necessarily fresh either. The cans and bags they’re supplied in have an expiration date but I haven’t noticed much enforcement of that concept. I’m not sure anyone but the suppliers are concerned with that anyway.
I don’t care. I’m only going to take 3 or 4 drinks out of it anyway.
I’ll drink either one. I prefer Pepsi, because it has a little bit of vanilla flavor. My top choice would be Boylan’s diet cola, but the only place that served that around here closed. 
I’ll drink any of the basic colas. I only get picky when I order the diet version. There, any one is acceptable EXCEPT Diet Coke, which is Satan’s ball-sweat.
Why do we always assume Satan’s ball sweat tastes unpleasant? For all we know, it’s delighful.
mmm
When I was drinking colas and I was asked if Pepsi is OK, my response was ‘No, I’ll have an iced tea.’ No Pepsi. Coke!
[NB: The last couple/few years when I was still eating fast food, I’d have to specify unsweetened iced tea, which used to be the default.]
And sewer rat may taste like pumpkin pie, but I’ll never know.
I will order either a diet Mt. Dew or Diet Dr. Pepper. If neither is available, iced tea.
No, that’s Coke. Pepsi is sweeter, has a richer flavor, and lacks that battery acid kick.
If i ask for a coke and I’m offered a Pepsi, I’ll switch my order to ginger ale. If they don’t have that, either, I’ll get water.
I’m very sensitive to caffeine, and it’s an indulgence for me, that I’ll pay for later, to get a caffeinated drink after breakfast. I’ll sometimes do it for coke or tea. Not for Pepsi.