The 5e Alchemy Jug (on page 150 of the Dungeon Master's Guide) has several uses. Some are common and useful, like water, poison, acid. Some are natural ingredients and liquids, like honey, vinegar, oil. Some are alcoholic beverages, like wine or beer.
And then there's Mayonnaise. It is a complex condiment (requires, among other things, mustard, which is another complex condiment).
Why? What's the point? I figured maybe it was there as an example of what the jug could create, but the rules explicitly say to name one liquid from the table below. Is there some use of mayonnaise that is relevant for the game? Or were the devs just having a laugh?