Peter speaks of the punishment that the false teachers will receive as if it were a reward. Alternate translation: "receiving what they deserve for the harm they have done" (See: [[rc://en/ta/man/translate/figs-irony]])
Here the word "luxury" refers to immoral activity that includes gluttony, drunkenness, and sexual activity. Doing these things during the day indicates that these people are not ashamed of this behavior.
The words "stains" and "blemishes" share similar meanings. Peter speaks of the false teachers as if they were stains on a garment that cause shame for those who wear it. Alternate translation: "They are like stains and blemishes on clothes, which cause disgrace" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-doublet]])