Matt Rife Tells Ghost Hunter with Autism to Kill Himself, Comedian Claims He Was Being Bullied

Matt Rife may not be a specter or spirit -- but he's now in the crosshairs of the ghost hunting community ... because he told a paranormal expert with autism to kill himself.

Here's the deal ... Matt and his collaborator, Elton Castee, posted on Instagram an upcoming event at the Haunted Warren Museum -- a paranormal spot the pair purchased last year that's best known for housing the demon doll Annabelle.

Self-described P.I. -- that's "paranormal investigator" in this case -- Chris Mac responded to the post by giving an online sermon on the Salem Witch Trials ... which for reasons unknown led Matt to rip into the "lifeless douchebag" by saying, "please remove yourself from this earth."

Chris responded to the attack on Facebook, saying ... "Now am going move forward with all this nonsense garbage what Matt said and Elton Castee control your mentor Matt or get Matt therapy I don’t want ever ever want see Matt bully a person with autism again do I make myself clear not ok to say with a person with autism I have autism."

A source close to Matt tells TMZ ... the comedian is relentlessly bullied in the comment section of his posts with "vile" remarks attacking him. We're told Matt responds to the trolls, and then the troll deletes their comment. The source said there is context missing from Matt's exchange with Chris since the comments are deleted.

There's no evidence from the comments that Matt knew Chris had autism.

Chris doesn't have a large following on social media -- but his loyal followers and friends are now haunting Matt after the nasty attack ... not exactly a new phenomenon since Matt has been dogged by members of the community for a while now who think the popular stand-up comic is only into ghost hunting for the money.

Matt and Elton charge people up to $166 for admission to the Haunted Warren Museum -- and that has pissed off a lot of people in the paranormal community, who investigate these cases out of passion, not money.

We've reached out to Matt's rep ... so far, no response.