Well, it wasn't just your run-of-the-mill, ordinary cup. From a Bloomberg article, a Chinese collector recently purchased an ancient ceramic cup for $281 million HK dollars, which translates to approximately $36 million USD. Like I said, not your average cup that you find at Ikea.
The best part? He used his American Express Centurion card to make the purchase, meaning that he was able to accrue points, to the tune of a whopping 422 million! Before you freak out, these are Hong Kong Amex points which means that they transfer to airlines at a ratio of 15:1 instead of 1:1, meaning that this translates to the equivalent of ONLY 28.1 million US Amex points. For us points and miles enthusiasts, we can only dream of the potential uses for that many points, which alone would be enough for about 200 round-trip tickets in First Class!
Even though the Centurion card is a charge card and thus has no fixed spending limit, he had to swipe it through 24 times since the system will only permit transactions up to ~$1.5 million USD each. Amex has declined to comment if this is the biggest transaction ever made on one of their credit cards, but I can't imagine what would top it.
So there you have it, good to know that no purchase is ever too large to use your Amex charge card for.