There is no way that Tony is going to admit that he is jealous of every person that stands or sit closer to him that Tony does at that moment. McGee knows this and he likes that piece of knowledge. So when ever Tony is teasing him or doing something that he shouldn't do Tim moves and goes stand closer to someone else.
Like right now. Tim was explaining something vital to the case to Tony and Ziva, and Ziva listened, asking questions and well, being polite, but Tony? Tony takes childish to a whole new level. He makes an innuendo of everything that Tim says and he keeps grinning and doing that weird squiggly thing with his eyebrows.
Suddenly Tim decides he's had enough and he moves closer to Ziva. He takes satisfaction in the fact that Tony's expression changes to jealous in two seconds flat, he sees it all happen in the reflection of his screen.
Tony starts paying attention and Tim rewards him with moving closer to his lover. Every inch he moves closer Tony's smile gets bigger, and the moment they can make contact Tony's hand moves over his back and stays there until Tim is done explaining.
It's their own little game they play and the both love it!