Kelly Clarkson Trashes Dr. Luke ... He's a Bad Guy

Kelly Clarkson went nuts on Dr. Luke, saying he's a terrible person and that she was "blackmailed" by Sony to work with Luke ... similar to claims Kesha has been making.

Kelly was on KIIS FM in Australia Monday and said she likes everyone she works with ... except Luke. She says they've clashed in a very bad way and he's a known liar.

DJ's Kyle and Jackie O pressed Kelly about Kesha's rape claim, but she says she's had no similar experience with Luke and couldn't judge.