RJ Mitte thinks mass murder is really funny ... because he got a good laugh over the woman who claims she murdered between 22 and 100 people.
The "Breaking Bad" star was leaving Pinz Bowling Center in the San Fernando Valley Monday night when our photog asked him about the Craigslist killer. He genuinely thinks Miranda Barbour is "hilarious" -- a real-life Dexter he says.
But wait ... there's more. RJ says even though it's messed up, there should be more killers like Miranda.
RJ seems to have been influenced by his fake dad ... he's a nice guy, but man this is weird.