I wonder what happened between Tony and Gibbs when they first met. Given how Abby and Ducky feel about Tony and act around him, I get the feeling that there was this little foursome who got cases solved for a while. Then along came others.

There's definitely a father/son vibe going on with Gibbs and Tony IMHO as well as teacher/student and friend/friend. I think Tony never wants to disappoint Gibbs, practically breathes for a "Good work, DiNozzo" compliment from Gibbs. It's probably the only way Tony knows how to behave with someone he sees in that light?