The former 'N Sync heartthrob was the latest target of Amanda's venom Thursday, after he publicly said the former Nickelodeon starlet has some psychological issues to sort out.
"It's one of those situations where obviously there's some mental problems there and she's not able to see that -- we all are," Bass told the Las Vegas-based radio show Mark and Mercedes in the morning.
She wrote, "I ignored Lance Bass on twitter and now he is saying I have a mental illness. Sorry you're an ugly ex boy band member w/ no talent or career. I haven't spoken to Lance Bass in 11 years. To say I have a mental illness out of nowhere makes me lash out! You're making me crazy!" (Not the best argument, Amanda.)
Bynes and Bass do go back some, as he produced her 2005 film, Love Wrecked.
In recent weeks, Bynes has used the term "ugly" in her attacks on a number of (attractive) celebs, among them Rihanna, Courtney Love, Sports Illustrated model Chrissy Teigen and Playboy Playmate Jenny McCarthy.
Elsewhere Thursday, Bynes re-tweeted a note from Chelsea Handler sidekick Chuy Bravo that he's following her; and a follower's jab at Love after the rocker told Howard Stern she thinks she could help Bynes in her ongoing problems.
We're not sure what Amanda's gonna say or do next, but whatever it is, we'll have it right here for you on RadarOnline.com.