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. What reason have the designers given for adding it? Is there some use of mayonnaise that is relevant for the game? Or were the devs just having a laugh?
Best Answer
Funnily enough, Christopher Perkins goes into exactly this topic during his 'Storytime'1 speech at PAX South 2017.
Summary: Being exhausted and angry about broken air conditioning at WOTC led to them making up a list of silly liquids for the Alchemy Jug. Mayonnaise eventually was the only survivor of said list (while many others were too inappropriate to keep) because they wanted to eventually hear the hilarious stories of how covering someone in mayonnaise achieved a goal.
Transcript from the speech, to the best of my abilities:
1: In case VOD link does not start at the proper time, the relevant part starts at 31m58s.