Pointing to data showing run-ups in foreign purchases of U.S. stocks before the 1987 crash, the dot-com bubble in 2000, and the 2008 financial crisis, Ed Yardeni wrote in his eponymous research newsletter, "Their buying has a record of being a contrary indicator. They tend to be big buyers right before bear markets."

While Netflix could see its subscriber numbers drop during a downturn, some bulls suggest the streaming service might be one of the last things people are willing to give up when their wallets get lighter.

"Tariff" has probably been the most used word in the business and investing world since U.S. President Donald Trump announced his new tariff plan on April 2.