The term "negro" was a commonplace descriptor when "Paul's Case" was published in 1905. It is no longer in popular use and can be considered offensive.
A stenographer is a transcriptionist trained in shorthand when taking dictation. Although less common now, this job used to do what voice-to-text software does today.
"in order to curb his appetites and save the loss of time and strength that a sowing of wild oats might have entailed..."See in text(Paul's Case)
"Sowing Wild Oats" is a colloquial expression that stands for the act of dating many partners before marrying. Basically this young man did not date around like most young men would prior to marrying.
Intense, extreme, gaudy, or flashy description. For example, Oscar Wilde (an aesthete just like Paul) was accused of such type of detailing in *The Picture of Dorian Gray. *All items in the novel are depicted so richly that they caused distaste to the prudish Victorians.
"Hauteur" means arrogance or snobbery. She did this to hide her shame about the tickets being handed down to her. In the end, this act and the fact of the tickets renders her even less impressive in Paul's eyes.
Flippant means disrespectful or frivolous. The choice of flower is demonstrative of a want to show off and appear to be better than everyone else. To add to it, the choosing of the color red (see previous "red" annotation), is intentionally made to select a color that still calls more attention to itself due to its bright, showy nature.
