"Big Brother" contestant Jason Dent thinks rape is seriously funny -- he went full LOL while talking about having sex with another housemate's wife ... while forcing the guy's kids to watch.

The footage is pretty disturbing ... Jason was cracking up on the Internet live feed Monday, joking he was going to f**k Kevin Schlehuber's wife if Kevin turned on him in the game. A female housemate, Alex Ow, was laughing along as Jason joked he'd also tie up Kevin's daughters and "make them watch."

Fair to say ... the 'BB' house is getting out of control. Remember, Jason also made a rapey comment earlier in the season -- saying he'd hold down a female housemate so other guys would be able to 'backdoor her.' Not to mention the rampant butt and genital poking that's been going down.

Interestingly, a few weeks ago Alex got upset about the sexual shenanigans because she has a family member who'd been raped. This time around, she was totally lighthearted.