A state of being that is somewhat related to being hungover but with fewer specific symptoms other than a feeling of general "icky-pooness." To the extent that there are known symptoms, they may include indecisiveness, lethargy and mild dizziness. Basically, when you wake up feeling drunk but probably don't have a high BAC, don't need to throw up but do REQUIRE food (specifically bacon), you can be said to be feeling mayonnaisey. Mayonnaiseyness is usually gotten rid of by eating greasy foods, minor day drinking and just waiting it out.
var. Mayonnaisey can also be used to describe things that are generally unpleasant like bad weather, a boring movie, or a yucky meal (see examples below).
Girl #1: "Hey girl, fun time last night! Wanna meet up and grab some breakfast?"
Girl #2: "Sure; I'm feeling pretty mayonnaisey so I'm going to need to hit up a McDonald's or that greasy spoon down the street."
var. "It's sort of raining outside; how mayonaissey!" "The movie was so boring, I almost fell asleep. I haven't seen a movie that mayoniassey in a long time." "That lobster was clearly frozen and they put way to much sauce on it. It was almost as mayonaissey as the fish we had last week."