Although Kim had joined in on the interrogation, it seemed that she might have known who did the deed all along.
"I think I know who it's from," she teased.
"Just let me live!" Kourtney told her sisters. "Don't analyze."
The mother of four opened up about her frustrations in a confessional.
"My sisters are pretty nosy when it comes to anything in my life," Kourtney said. "I don't know if they're bored in their own lives and they want to live through my wild dating life that they think is going on. Like, come on guys. Let's get it together."
As for who gave Kourtney the hickey, it looks like we'll have to wait until the new episode of "Keeping Up with the Kardashians," which airs Sunday night at 9 p.m. ET on E!