In 2014, Griffin was asked on Twitter who was the "biggest douche celebrity you've met?"
"Probably Debbie Lovato. Plus she should calm the f down bout Lady Gaga getting barfed on," Griffin wrote.
Then in August 2015, she had a crack at her singing at the VMAs.
"Demi's live singing was very obviously live if you know what I'm saying. And then the rest of the track or tracks #atleastshesang-ish," she wrote.
Griffin told Ryan Seacrest that she felt like she was bullied by the singer's Lovatics fanbase. She said she received death threats and had to get the police involved.
"As you know, I'm an equal opportunity offender," she said, "but this is the first time that I know of that a comedian of my stature, has actually been confronted this way via social media by the artist herself, knowing she has 30 million Lovatics."
It comes as actor (and famed Donald Trump impersonator) Alec Baldwin took to Twitter to defend the under fire comedian.
Baldwin, who is used to copping barbs from the US president, urged Griffin to move on from what she called bullying from the Trumps.
"Kathy ... f**k them. F**k them all. No 1 believes u meant 2 threaten Trump. Trump is such a senile idiot, all he has is Twitter fights," Baldwin tweeted.
"Ignore him. Like the leaders of all the other countries in the world. Ignore him."
Baldwin alluded to his own 1998 call to stone then Republican politician Henry Hyde to death on Late Night With Conan O'Brien.
"No one walked out of the studio and said, 'No! We're serious!' No one," he tweeted.
"But all your gutless, weasels in the GOP insisted that I actually threatened Hyde. They played the victim beautifully."
Baldwin's impersonation of Trump on Saturday Night Live has also earned him ire from the President, including late-night tweets that the iconic show is "unwatchable ... totally biased, not funny."
