real Chinese snake oil was essentially some kind of omega-3 rich thing for topical application.

And, from the wikipedia: http://en.wikipedia.org/wiki/Snake_oil

"snake oil" as sold in the US was essentially capsaicin, which is used today, both as a topical treatment and others, for a variety of muscle/bone/tissue ailments. http://en.wikipedia.org/wiki/Capsaicin#Medical

Whereas snake oil in cryptography tends to be worse. In practice even snake oil algorithms are probably enough protection for short-term, limited use (no one is going to devote real cryptanalysis resources to high school notes), but it can encourage people to have a false sense of security and do things they wouldn't otherwise, or it ends up getting used for purposes not originally intended.