You would use this word to describe a situation wherein you are, for example, at one second enjoying a pleasant conversation and washing your feet in the shower and the next thing you know all of your fleshy bits are out and someone has you bent over the soap dish. This sudden burst of nakedness could be a testament to the one removing your clothing (they are very smooth and have you from done-up to undone in 3.5 seconds). Or it could simply be gaps in memory related to alcoholism that prevent you from remembering the awkward fumbling that actually did take place. 11/10 times it will be the latter.
Spontanudity is majestic and satisfying in inexplicable ways and has been scientifically proven to make sex seem 127% better than it might otherwise be.
However, poorly executed attempts at spontanudity can result in an irrecoverable loss of pride and lifelong social shame.
Cooler girl: Stop speaking now. That sounds simply attrocious and I feel very sorry for you. I had a great night out with the mates which culminated in a passionate bout of spontanudity
Boring girl: My sex life is a joke.