I would wager that you'd end up being handed a can of Coke at good proportion of the time.
"Oh sorry, they don't serve Pepsi here."
Richard Stallman's way makes it clear that he does not want to support Coke. He does not want you to hand him a Coke by mistake. Since I assume that is his goal, he communicated it well.
His story helps you to notice, and remember, this seemingly trivial detail.
I'm confused why you think him saying "I only want Pepsi" is in any way clearer than my saying "I only want Pepsi".
EDIT: Make it clearer by saying "Pepsi (absolutely not Coke or any other brand)" by all means but the person buying the drink wants to make sure you get what you want and then get on with their lives, they're really not interested in the why.
It feels to me that Stallman wants to use this - as with most of what he does - as something of a polemic about what he believes. That's fine but it does make the whole document less clear about the actual detail of what he wants.
Stallman's "I want pepsi" reads more like "I specifically don't want Coke, and Pepsi is the most common alternative". With that information in hand, I'd probably suggest he try some of the more boutique cola brands that are available. Your "I only want Pepsi" reads like "I specifically want Pepsi", without accounting for regional flavour differences, etc.
I wouldn't supply anything other than Pepsi for fear of needing to know the history and practices of the local company that makes the soda I thought would be a fun surprise for rms.
You know that an instruction can be short, unambiguous, accompanied by best designed clear easy to understand diagram / logo, and that someone will ignore it and do something terrible.
"A few cans of Pepsi (NOT COCA COLA (http://example.com) and not any diet product please)" does have the advantage of being more check-list like, allowing people to hghlight / crossout the items they've done or not done yet.
The post-mortem of a kickstarter posted to HN yesterday, where someone managed to print and deliver a poster with a misspelling of the word "BROOKLYN" as "BROOKLYIN" has made me think about how people find and prevent errors.
HN isn't a good audience to ask that question because there are different ways to write code. There is only one way to write BROOKLYN.
While semantically your suggestion may seem equivalent to his, there's a big difference between saying "My cola of choice is Pepsi" and "I equate Coca Cola with murder".
I totally agree. Look at his bit about parrots (part of a larger bit about pets):
>DON'T buy a parrot figuring that it will be a fun surprise for me. To acquire a parrot is a major decision: it is likely to outlive you. If you don't know how to treat the parrot, it could be emotionally scarred and spend many decades feeling..
This right here is why I can't stand RMS. He's putting together a rider for all his (borderline unreasonable) demands when he speaks. And even when he's adding irrelevant things, he still manages to be a condescending know-it-all who has to tell you why your decisions are wrong, and why the way he thinks is the correct way to see things.
I don't know why you have to read that clause that way. I thought it was amusing, (though it appears he wasn't amused) the only reason he would have put that clause in there is because someone actually bought a parrot because they thought he would like it. I imagine it probably didn't happen in the US, but in a country where parrots don't cost as much as a month's wages.
"Oh sorry, they don't serve Pepsi here."
Richard Stallman's way makes it clear that he does not want to support Coke. He does not want you to hand him a Coke by mistake. Since I assume that is his goal, he communicated it well.
His story helps you to notice, and remember, this seemingly trivial detail.