Fluffy Puff Mayo
From Homestar Runner Wiki
Fluffy Puff Mayo is a product that appears to be made from Fluffy Puff Marshmallows, though if it were made completely from marshmallows it would actually be marshmallow fluff (a nearly imperishable product with a long history; commonly enjoyed on a sandwich with peanut butter, aka the Fluffernutter), not mayonnaise, which is made from vegetable oil, water, and egg yolks.
It first showed up in the toon Where's The Cheat?. It can also be seen in Meet Marshie and in the Strong Bad Email the bet. In the latter, The King of Town had two jars of it in his pantry. It also appears as an advertisement before A Decemberween Pageant.
Its advertising slogan is "Made From The Best Stuff!", which may be a reference to Snapple, which advertises itself as being "Made from the best stuff on earth."