As Ziva said, Tony originally used "Sweet Cheeks" in Undercovers when they were pretending to be married assassins. It was interesting that Ziva called Tony "Mon Petit Pois" in return and not "My Little Hairy Butt." She used both in Undercovers. Anyways, I don't see any of these becoming permanent nicknames between them. They were reminiscing about what must now seem a different world to both of them.
McGee also called Ziva "Sweet Cheeks" in the episode Blowback when they were chasing Charles Harrow. Tony has called Ziva many nicknames over the years, but I think my favorite is "My Ninja" from Nine Lives, and the other times he has used Ninja to describe her. Ziva doesn't really seem the type to use nicknames. Has she ever given one to Tony other than in Undercovers?
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