Volcano Sauce is a mixture of Kewpie Japanese Mayonnaise, Sriracha sauce, and vinegar. It is excellent on oven-baked sweet potato fries, even when some of those fries are a little burnt. I hear Kewpie has MSG, but it's also delicious. So there.
(photo by DanF)
p.s. Thanks to Jane, who told me about the Kewpie mayo.