At least as old as 17-May-1992 01:33
[OPSEC is short for "Operations Security", i.e. ensuring a potential enemy cannot guess what you're about to do.]
From "The OPSEC Indicator", Fall 1991:
PIZZA INTELLIGENCE: AN UPDATE
Earlier this year we reported that Domino's Pizza claims it can predict when the government is about to undertake some sort of major activity based upon the increase in pizza deliveries to the Pentagon and the White House. Pizza orders increased substantially just prior to troop deployments to Grenada, Panama, and the Middle East.
According to The Washington Times of August 21, 1991, during the early hours of the abortive Kremlin coup in August, Domino's "Pizza Meter" registered 102 deliveries to the Pentagon, breaking the Gulf War record by one; the White House ordered 52 pizzas, breaking its Gulf War record by seven.
The CIA, by contrast, learned its OPSEC lesson: There were only two orders, and they were quickly cancelled.