The tradition has become something of a national ritual, and it's born out not only in folklore, but also some data. Interest in Chinese food spikes considerably each and every year on Christmas, as evidenced by Google search trends. No other day during the year compares, or even comes close.
Notice the visible spike in searches for "Chinese food" last year on Christmas day:
And again in 2012:
And in 2011:
And in 2010:
And in 2009:
The same bump emerges each year, dating back at least to 2004 (the earliest year for which Google trends data is available).
It's hard to prove that those searches are driven purely by a desire to eat Chinese food. But anyone searching for Chinese food on Google will see in the results a slew of review and menu sites, such as Yelp and Menupages.
In addition, online delivery service GrubHub has noted a very clear and significant jump in sales at participating Chinese restaurants on Christmas.
Jews, of course, are not the only ones eating Chinese food on Christmas. But few cultures or religions are as famous for the practice in America.
The annual tradition, sometimes called 'Jewish Christmas,' has become so widespread that according to Plaut, even Orthodox Jews now participate flocking to the country's growing pool of kosher Chinese restaurants, which forego the pork and shellfish, on Christmas. There are how-to guides for celebrating 'Jewish Christmas' (i.e. where to find the best Chinese food in New York City and Washington D.C.); there are entire reddit discussions dedicated to uncovering the origins of the tradition; there are even songs, youtube videos, and memes that poke fun at the peculiar habit.
Why exactly eating Chinese food on Christmas has become a pillar of the Jewish Christmas experience in America is unclear. There's the fact that few other places are open for dinner that day. And it's a way to make the day still feel special in some way.
And then there's the long-held affinity for Chinese food among Jewish Americans throughout the year, not just on Christmas, according to Plaut. Jewish comedy has made fun of family meals at Chinese restaurants since at least the 1950s, he notes in his book. A 1992 paper by Gaye Tuchman and Harry G. Levine establishes a similar long-standing affinity, and credits part of it to the convenience of the cuisine, at least for those living in New York. "In short, quality, price, and proximity are some of the reasons why Chinese food became so important to New York Jews."