Bulma just ignored Chi-Chi as she shoveled a mountain of egg salad into her mouth while watching her morning soaps. This was her morning routine: make breakfast, feed Chi-Chi, and eat her food while watching tv. Then she'd repeat the same actions throughout the day for lunch, snacks, and dinner. It may have only been two months, but Bulma was definitely taking to her new lifestyle of laze and excess.
It all started when she decided to visit her old friend one day. No one had heard from her in months and Bulma was worried something might be wrong. She rang the bell and knocked for ten minutes or so before finally kicking in the door and barging in. It was then that she was bombarded by the noxious smell she would soon become accustomed to. A greenish haze filled the air that made Bulma gag and her eyes water. She called out for Chi-Chi, but got nothing in response. When her eyes adjusted, she was able to see the mountains of trash and fecal matter that adorned the hardwood floors. She slowly made her way through the filth when she heard strange noises coming from the kitchen. She made her way in and saw her friend; at least she thought it was her friend. There was a fat, dirty woman on all fours eating from a pile of random, rotten food. Bulma tried to get her attention by talking to her, but had no luck. She eventually realized that something very wrong had clearly happened to Chi-Chi. There seemed to be no sign of human intelligence in her. She was a machine, an animal, that only lived to eat.
Bulma initially planned to take her to get help, but couldn't get Chi-Chi's new obese frame through the door. She thought of bringing either Goku or Vegeta to help the poor girl, but couldn't bring herself to do it. She felt bad for Chi-Chi and didn't want to humiliate her in front of the men by letting them see her in this pitiful state. So she decided to take care of her.
Bulma tried to help get Chi-Chi back to normal. She bathed her, fed her, and cleaned up the house. She tried to teach the dumb girl to speak again and potty train her, but none of it really stuck. She realized that the struggle wasn't worth it and that that the real Chi-Chi had been lost forever. Not wanting to leave this helpless slob alone, she started to look after her like a pet, instead of a person. It no longer made sense to think of her as anything other than a dumb animal.
Unfortunately for Bulma, that dumb animal had been changing her more than she realized. Bulma constantly had to get food to feed her new pet, and having all that fattening grub around started to affect her. She gained weight, got lazier, and was always gassy. Since Chi-Chi was in no position to judge her, she started to care less and less about her etiquette and personal hygiene. She gave up trying to clean after two weeks. The next two months saw her getting nastier and nastier. She never changed her clothes, even though they had grown far too small for her. She stopped brushing her teeth, doing her hair, and bathing. The toilet was no longer needed in the house, since Chi-Chi left shit piles all over the floor. Bulma would just squat over one of those to do her business, growing increasingly numb to her behavior and surroundings. Most of her time was spent sitting on her widening ass, leaving a permanent impression in the couch, watching the most mindless programming tv had to offer. She didn't know how this dramatic change had happened, but she was too lazy to think too much about it. She just watched tv and rubbed her bloated belly as she filled it with egg salad, burping and farting as she did so.