I've run against a few Vader shuttles recently and run into two rulings on the card: one is that "you" refers to the player, not the shuttle, so any attack from any ship on your sidecan trigger it. The other is that "you" refers to the shuttle specifically, so only its attacks can trigger Vader. Which is correct?

It refers to the shuttle only. Your friends are terrible people.

Rulebook page 19:

Many card abilities use the word “you” to specifically reference that Ship card. Abilities on Ship cards cannot affect other ships unless explicitly specified by the ability.

...

Likewise, Damage cards and Upgrade cards only affect the ship to which they are assigned, unless otherwise specified.

Technically the word "you" from the Vader card is not on a ship card. So the second sentence does not apply. The last sentence does.

"You" does not refer to the player.

Like I said - it refers to the shuttle.

Thanks, all. That relieves me