The 40-year-old comedian recently named Bieber as the worst celebrity she has ever interviewed.
"He was trying to flirt with me and it was so uncomfortable," Handler said at the Variety Fandango Studio presented by Dockers at the Sundance Film Festival. "Like, that's his shtick. He would come on and flirt with you, and you just felt like a child molester right away, and I was like, I don't want to feel that way."
Handler interviewed Bieber multiple times on her former E! talk show, Chelsea Lately, including in 2010, when a then 16-year-old Bieber repeatedly asked the host on a date.
He returned on Valentine's Day in 2011, giving Handler a lingering kiss on the cheek. Though it's worth noting that Handler gamely flirted back.
The always outspoken Handler also opened up about her new Netflix Show, Chelsea Does, a four-episode docuseries focusing on more serious topics like drugs and marriage. Handler talked about what's sure to be one of her most controversial episodes, delving into racism in America.
"Everyone's racist," Handler says. "I mean, everyone is, and I wanted to do the thing on racism because I wanted to go at it lightly. Like, I don't want to be so serious about everything, and political correctness is so overwrought. And I thought, let's do something fun with this, even though it's such a serious, sad topic. Let's go at it, with like, a sense of humor."
ET sat down with Handler last week to chat about her buzzworthy new show -- which premiered this past Saturday -- when she mentioned her potentially awkward run-ins with the Kardashians, given that she poked fun at the family for years on Chelsea Lately.
"I see those girls all the time, so they either have to get over it or not," Handler said bluntly. "I ran into Kim at a friend's house, and sometimes I run into her and I'm like, 'Oh no! Here she is.' Then I have to be like, 'Hey, Kim!' after all the stuff I've said. But you know what? I just have to stand up and take it, and go, 'Listen, I know that I said stuff.'"