Lowndes's character Adrianna is currently embroiled in a feud with Silver (Jessica Stroup), who is dating her ex-boyfriend Navid.
Steger, who plays Navid, has now told TV Line that the situation will escalate when the group flies to Mexico.
"We all get in the plane to head to Cabo, and Ade just shows up," he said. "There's a bit of a catfight in the private jet, and it's probably the cattiest episode between the two."
Lowndes added: "There's actually a lot of catfighting. Ade decides to fill a bottle with contaminated tap water and makes Silver sick, after which she replaces my sunblock with moisturiser and gives me the worst sunburn of all time. Plus, we get to wrestle in the pool!"
Stroup has previously suggested that Adrianna will tamper with Silver's medication in a future episode, which will mean that she begins to struggle with bipolar disorder again.
90210 airs on Mondays at 8/7c on The CW in the US and on Tuesdays at 9pm on E4 in the UK.
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