Argthtjtr

Ashnod's Coupon has the ability:

{T}, Sacrifice Ashnod’s Coupon: Target player gets you target drink.

Errata: You pay any costs for the drink.

Meanwhile, R&D's Secret Lair says:

Play cards as written. Ignore all errata.

Ignoring the fact that R&D's Secret Lair now has errata to make its mana producing ability still work (which is baffling to think through), how does R&D's Secret Lair interact with Ashnod's Coupon? The issue with Ashnod's Coupon is that the Coupon's errata is printed on the card. Thus, it is errata (so you should ignore it) but is also part of the card as written (so you should use it). Which one happens?

Everything in this answer is under the rules caveat on silver bordered cards:

Silver-Bordered

Cards in certain sets and certain promotional cards are printed with a silver border. Silver-bordered cards are intended for casual play and may have features and text that aren't covered by these rules.

As a result of this rule, Wizards does not publish official rulings on silver bordered cards. MaRo claims to be Magic's "Silver Bordered Rules Manager" (as mentioned in the FAQs for Unhinged and Unstable), but I want to stress again that the "officialness" of this is up for debate, as the Magic rules absolve Wizards of having any official opinions on how silver bordered cards work.

MaRo's ruling on the subject is that the owner of Ashnod's Coupon still pays for the drink:

R&D Secret Lair contradicts itself as it asks you to play “all cards as written” and “ignore all errata”. Ashnod’s coupons errata is written on the card.

This means I can basically rule either way so I have opted to rule in favor against dumb shenanigans. (Note I’m all for regular shenanigans when playing with Un-cards.) Owner of the Ashnod’s Coupon pays for the drink.

My personal opinion is that "Ignore all Errata" is its own sentence, and thus can function as an independent part of the ability: first, play all cards as written, and second, ignore all errata. Under this interpretation, the errata on Ashnod's Coupon is nullified by R&D's Secret Lair, and the target player will have to pay for the drink.

However, even under this interpretation, a player can still conceded the game at any time. Thus, this combo, targeting a sufficiently expensive drink (such as a bottle of 50-year Macallan, retail price $30,000), effectively becomes "Target player loses the game". This makes it a 2-card 0-mana win combo, which I believe makes it the simplest first turn win combo in all of magic.