The 30-year-old model defended the 29-year-old designer in a series of tweets Monday after Cavallari faced heavy criticism for her sons' thin appearance.
"I will never know why parents criticize others so harshly, knowing they'd go insane if they were on the receiving end all the time," Teigen wrote.
"No parent out there thinks they're perfect. I loathe these [expletive] commenters. Who would want to make someone feel horrible for fun?" she added. "Anyway, love you @KristinCav and screw everyone's bored [expletive]!"
Cavallari had come under heavy fire after posting a photo of her sons, 3-year-old Camden and 2-year-old Jax, on the Fourth of July. Many social media users deemed the toddlers too thin and mom-shamed the designer in the comments.
"Yep, I starve my children. Just blocked the most people I've ever blocked in my entire life. Happy 4th hahaha," the star wrote Sunday in response to the controversy.
Teigen herself faced backlash in April after going on a post-baby date with husband John Legend. The model was spotted at dinner nine days after welcoming her daughter, Luna, and subsequently defended herself on Good Morning America.
"We needed a break. We needed to go enjoy each other's company and be out," she explained. "We were gone for an hour. We had a good meal together. I think happy mommy, happy daddy, happy baby."
"I used to read mommy blogs like crazy so I knew mommy shaming was a thing, but I didn't think that it would come from going to dinner," the star admitted. "[The criticism] just kept going on and on."
Cavallari married NFL star Jay Cutler in 2013 and is also mom to 7-month-old daughter Saylor. Teigen wed singer John Legend the same year.