As with the vampire-to-lawn-chair problem, it involved Matter magick in Mage 1e. One of the examples listed of "coincidental magick" for Matter was "transmuting bullets into air" with the coincidence of "the gun was never loaded." Now, earlier examples in the book of coincidental magick in the book suggested that to be coincidental magick, the coincidence had to be something that could occur, even if unlikely. Bullets do not, on their own, turn into air, so a lot of time and Internet bits were spent trying to rationalize these two… ahem, Paradoxical things.
The canonical example became "Can you heal the damage from a bullet coincidentally by pulling a whiskey flask from your pocket (as is suggested on page 248 of the 1st Edition Mage: the Ascension core rulebook) even if neither the flask or pocket was there before?" After all, both of those things are reasonable. Does the Consensus collude with you to make it happen with something like Matter, or even Life 2? Or do you need to actually conjure a flask with Matter and Prime for that to work.
This was considered a hot topic of discussion as far back as, again, 1994. The online FAQ for Mage back in 1999 addressed the issue only vaguely, and Mage players on the Internet developed the HAP/HOP/[^HYP]/RBD/PBD system of talking about Paradox to cover it. Stephen Lea Sheppard, Mage author (and former "Freaks and Geeks" actor) explains:
HAP\HOP\HYP|RBD/PBD is a way of categorizing different approaches to running magic in oMage. HAP/HOP/HYP is one axis, and RBD/PBD is the other.
Axis The First
HAP/HOP/HYP is a method of determining whether effects are vulgar or coincidental. In its simplest form, it's a way of addressing the question "Can reality see into your pockets?"
Say you want a business card to hand to a guy you just met. You don't have one. You do have Matter 2 and Prime 2, though, which will let you create one from nothing. If you create a business card in your pocket and then hand it to him, with the coincidence "I just happened to have it in my pocket all along, really," is that coincidental, or vulgar?
According to the Hypothetical Average Perceiver theory, it's coincidental. This also lets you make a lucky whiskey flask, or do the "No, actually, I did remember to load my gun with silver bullets this morning" thing. It's supported in some places in the text of the game.
According to the Hypothetical Omniscient Perceiver theory, it's vulgar. Reality can see into your pockets. It's not possible to "coincidentally" create anything from nothing. The whiskey flask trick doesn't work unless you actually did have a whiskey flask, and just used whatever spell to make the bullet hit it and not you.
Harass Yonder Passerby is a joke. It's included in the HAP/HOP/HYP trinity because of tradition.
There are problems with both interpretations. On the one hand, if Hypothetical Average Perceiver works, then can I make money by summoning it into my wallet, even if there's nobody around to hear me when I say "Oh, look, I've got enough money to afford [whatever it is I'm trying to buy] after all!"? What about if I just summon the money into an empty room? Where does "Coincidental" end and "Vulgar without witnesses" begin under this model?
On the other hand, if you run Hypothetical Omniscient Perceiver too strictly, then suddenly no magic is coincidental at all. Reality saw the trajectory of that bullet, it saw your Entropy effect to adjust it, it knows you cast a spell, so that's vulgar. This applies equally to any spell you want to cast.
(I favor games that run under "loose" Hypothetical Omniscient Perceiver. My friend favors games that run on HAP.)
Axis The Second
RBD/PBD was created to explain the taxi.
So, I'm casting a Correspondence spell to move myself from one place to another. I want it to manifest as a convenient taxi that hits all the green lights and the driver forgets to charge me for the ride at the end of it. I could teleport, but that'd be vulgar, and I want coincidental. Can I do this, and if so, how?
According to Result-Based Determinism, the final result of the spell is all that matters. I can use Correspondence 3 to call up a useful taxi, as long as I'm willing to wait for however long it takes to show up (which is, usually, how long it takes for the spell to affect the nearest actual taxi and manipulate events so that it does what I want), as long as the only actual benefit I get from the spell, in the end, is that I get from point A to point B quickly and free.
According to Process-Based Determinism, I can't do this. Not with just Correspondence. Possibly with just Entropy, though, if I get enough successes, or, failing that, with Correspondence to locate the nearest taxi, Correspondence and Mind to ranged-mind-control the driver to me, Correspondence and Entropy together to plot a lucky course through traffic, Mind to mind-control the driver along the course, and Mind at the end to make him forget to charge me. Or, failing that, Prime and Matter to create the taxi, Prime and Life to create the driver, et cetera et cetera ad nauseum, and this last version ends up vulgar as hell.
I favor Result-Based Determinism, because it solves the Entropy Problem (which is, under PBD you can use just Entropy to do anything, because Entropy manipulates the chance of events to occur, and theoretically anything could occur), and because it goes nicely with "loose HOP."
The two most common types of oMage players on the Internet are Average/Process, and Omniscient/Result. They get into huge arguments. EDIT: Or they did, until we invented HAP\HOP\HYP|RBD/PBD on the Mage forum to stop them. Then they mostly got into arguments over which was official, until Malcolm Sheppard showed up and said "None. The writers don't think about this [stuff] nearly as hard as you all do. Christ." Or something to that effect.
And that's the tale of the whiskey flask: it's the symbol of Mage players trying to make sense out of poor explanations and contradictory game text in order to make the game they loved playable.
[^HYP]:"Harass Yonder Passerby," by the way, is: Find someone on the street outside where you're gaming and ask them if they'd believe your proposed magical effect to be plausible. If so, coincidental. If not, vulgar.