Flamboyant

Flamboyant; adjective; strikingly bold or brilliant.

From “The Yellow Wallpaper” by C.P. Gillman. “One of the most sprawling flamboyant patterns committing every artistic sin.” (second page)

In this passage, the narrator is describing the wallpaper that she encountered in the nursery room, where she was going to be sleeping in. She didnt like the aspect of the wallpaper, nor the design. To her, it was strikingly brilliant in a negative way, not a good brilliant.

Fatuity

Fatuity: Noun: something foolish or stupid : a foolish or stupid quality

From the short story “The Yellow Wallpaper” by Charlotte Perkins Gilman. “Looked at one way each breadth stands alone, the bloated curves and flourishes — a kind of  “Debased Romanesque” and delirium tremens — go waddling up and down in isolated columns of fatuity.”

I now understand that she was saying that the lines in the wallpaper were moving up and down and basically all over the wall in a stupid or foolish way. Sort of like they had a violent delirium and shook allover with tremors thereby it looked like it was all over the place.