Mr. and Mrs. Habit are the parents of Boris Habit. Though they never make physical appearances in the game, they are referenced several times by or in relation to their son.
(This page contains many spoilers for the late-game and story content, read at your own risk!)
Relationship to Dr. Habit[]
Dr. Habit's parents were a leading factor in his descent into instability. From his Diary Pages that can be found scattered within the Habitat, there's heavy implication of his parents having a dysfunctional life. The younger Habit describes them as sad people who are grimacing all the time.
Mr. Habit is implied to be a violent person despite the sadness and doesn't seem to care much for his son. Meanwhile Mrs. Habit isn't described much at all yet is blamed for an incident concerning the younger Dr. Habit, which can be interpreted as her being a toxic parent as well.
Habit implies in his first diary entry that they were doctors, and both of them push for their son to become a doctor. The attempts are rebelled against for a little while. Yet later on, Dr. Habit becomes a type of doctor - a dentist.
On the roof, there is a slideshow portraying the younger Habit giving his favorite flower (the Tooth Lily) a kiss, but as he did so was suddenly alarmed at his father's appearance at the door. His father is a silhouette with a wide, toothy grin. Habit says, "Dad?", and the next slide shows him with blood seeping down from the inside of his upper lip, implying physical abuse. Whether or not it was because his father had a dislike of feminine behavior from boys or his father had a more specific reason was left up to interpretation.
This encounter was briefly touched on in Dr. Habit's diary entries where he mentions kissing the flower so that it will grow. He does this in preparation to give the Tooth-Lily to his sad parents in hopes that they'll be cheered up when they have it.
Yet the damage his father had done was impactful - Dr. Habit wrote that the flower got hurt and his smile did too. Later diary entries say that some of his teeth were missing even as he reached drinking-age (whether or not the incident is the only cause isn't stated, but it's implied) and that the physical abuse incident happened when he was 10. He also blamed his mother for the incident even if her own actions weren't recorded, implying that she did something still hurtful but to a lesser impact than his father.
By the time he reaches drinking-age, their son still wrote that he wants them to be smiling instead of sad. However, he also wrote in the same entry that it isn't "fair" that sad people like them get to have full sets of teeth. This mindset is one of the motivations in Dr. Habit creating The Habitat, meaning his parents' toxic behavior is a huge factor in his own toxicity, despite not liking them.