I never claimed that 'owning a pen is vain'.

My comment referred to the GP's statement: Physical possessions like this pen is just so vain, shallow, and meaningless.

When I ask "Where is the cut-off", it's to prompt thought, to draw out an answer to the question: where is that cut-off?

  "obviously buying a $4000 pen…is utterly grotesque"

So where should the cut-off be? Is it $3500? $350? Where does the price of a pen become grotesque? If $4000 is obviously grotesque, where does that value statement become less obvious? Isn't that worth thinking about?

Another aspect to that debate are those who didn't buy the pen. For example, those gifted it in a will, or who win it as a prize. Or even of those who do buy it, perhaps an aspiring writer, who spends the entirety of their advance on this pen - not to signify or demonstrate their wealth - but as relief that they've finally been signed, as proof to themselves that they're not an imposter. Sure, it might not be the most practical use of their money, but does it justify the ad hominem of "grotesque"?

Yes, there is vast inequality in the world, and $4000 would be an enormous amount of money to a vast number of people. But if that's the argument, it doesn't matter whether it's a pen, a car, a house, a painting, an antiquity, a rare MtG card; the argument simply becomes: is it grotesque to spend $X when there's a cheaper alternative?