The first episode of NCIS starts out with an incident aboard Air Force One, where a Navy officer guarding the "nuclear football" is poisoned. While the Secret Service and FBI are arguing jurisdiction, Gibbs, Ducky, and Dinozzo board the plane and basically steal the crime scene.
They pull this off by having Ducky pretend to be the local ME, and Gibbs and Dinozzo pretending to be his assistants. This fools the FBI long enough to get them off the plane. A major plot for the rest of the episode is the jockeying for control over the body between NCIS/FBI/SS.
Except -- the FBI lead on scene was Fornell, who has a long history with Gibbs (they share an ex-wife, for example) and NCIS in general. In the later seasons (the ones I've seen) the two behave as if they had been friends for decades. They certainly have no problem with joint investigations when their jurisdictions overlap.
Is it ever explained in a future episode why Fornell didn't immediately recognize Gibbs when he got on the plane?