This guy gets punished by having his body parts replaced by alien parts under the effects of a drug that makes him submissive. He is a convict assigned to an experiment that replaces his body with alien limbs one session at a time.
The story has a powerfully atmospheric feel and features numbered "Decks" and a stratified society with caste indicated by deck of residence.
The protagonist known to us as "Buddy Joe" is fitted with a "alien suit" one part at a time, day by day, starting with a pair of "Grayish-green feet, webbed like ducks". Only the suit is not merely worn, it transforms his being.
The fitting is done under a drug called "Compliance" and is part of his sentence for "Rape". The phrase "Shouldn't have raped that girl" is used repeatedly to Buddy Joe by the other residents of his Deck (for he is free of confinement or other punishment when not being fitted with the suit).
The story includes a passage of Buddy Joe recalling his crime
He remembered the girl. He had cornered her in the lift. He remembered how she had shaken and wept.
but the rest of the memory is not what the reader might suspect (minor spoilers)
He had been thinking about his grandfather, and things he had said. The girl had a look that reminded him of his grandfather. That same questioning, intelligent look. He thought she would understand. Buddy Joe had asked her how it must have felt to walk under the stars when they shone high above, walk on the beach and feel the sand under your feet and the cool ocean breeze. And when she had asked him to stop he had ignored her and just carried on speaking, trying to get her to see.
Buddy Joe had raped her, pushed the hemispheres of her brain roughly apart and slipped the alien ideas into her head: let them congeal inside her. Dirty. filthy and without her consent.
All in all, a very memorable piece.
Possibly THE SPARROW by Mary Doria Russel.
Late in the novel the protagonist becomes a slave/pet to an alien and is physically disfigured. The flesh in his hands is cut away to make it seem that he has long elegant fingers to be more attractive to the aliens.