Once, during a workshop I was giving, one of the participants indicated they didn't know what I meant when I mentioned "purple prose." I gave the standard sort of answer:
Purple prose is another way of saying that the words and phrases you are using are too much for your subject matter - too colourful, too ornate, too baroque, too flowery, too exaggerated - and probably far too many such, as well.
Romance writing in the past lent itself to this kind of bad writing: her heaving bosom, his tumescent organ (or throbbing manhood), the aching void in her heart, their doomed love...
One self-published book, of which I read the first page, had no less than eighteen adjectives referring to colour (not just purple!) in the first two relatively short paragraphs, so that the reader thought they were sinking under the weight of a paint box. You know the sort of thing: Storm-grey clouds, indigo smudge of her eyes, crimson and russet leaves shining in the liquid golden rays from the molten orb of an autumn sun, etc etc. Guess what: I was not tempted to read on.
But my grandson has developed the art of purple
My daughter (in the garden) : It's time to go inside now.
Grandson: No, I don't want to.
Daughter: We are going in right now, darling.
Grandson: No! I'm not going to!
Daughter (scooping son up): Oh yes, you are.
Grandson (sobbing and struggling): You are ruining my life!
He's not impressed when we invariably crack up.