"Oh, it's on," Kim tells Khloe after the reality star's baby daddy takes a shot on social media.
In a sneak peek at Sunday's upcoming episode of the reality show, Kim tells Kourtney how she unfollowed Tristan on social media, before checking to see if he's done the same to her.
"I'm not following any boyfriend or anything, because it's so awkward when I have to unfollow," she explains. "You have to practically be married in at this point. That's my rule."
But when she takes a look at his page, she realizes -- with shock -- that he had apparently blocked her.
"He blocked me, what a f--king loser. Literally, what a fucking loser," she says, clear annoyance in her voice as she calls Khloe immediately.
"He blocked me on Instagram ... like, how old are you?" Kim says to her sister, about her man, over the phone.
"He's 27, only 27-year-olds know how to block," Khloe says with a laugh. "I don't even know how to block someone."
When Kim then says, "Oh, it's on," a concerned Khloe responds saying, "Please don't say the 'it's on,' what does that mean?!"
"It just means when I see him, I'm going to like spit on him," she jokes, before saying she thinks they can still "coexist" despite her anger. Khloe, however, isn't buying that. "I don't know if you guys can coexist, it's so crazy," she says.
Kim tells her she's probably right, before proving her point by saying "Your boyfriend's a f--king loser" again after hanging up the phone.
Watch the drama unfold Sunday nights at 9pm on E!