This very unusual expression was used—I am tempted to say “coined,” because I have never heard it before—by my friend, Bob Nightingale. He was describing a situation I didn’t see, myself, although I was there.
But I knew what he meant. Some offense had been achieved  to which the appropriate response was someone “flipping [him] the bird.”  It was just…you know…the right thing to do. In this instance, where Neo is flipping the bird at Agent Smith in The Matrix, it is an act with awful consequences.
Imagine, for instance, that some member of a group has done something that will be harmful to the group. He apologizes and the subsequent silence seems to go on and on. Why is that? It is because there is a predefined and expected response from the group. Because this response is predefined, the meaning of the silence is “We do not accept your apology.” The apology and the assurance of forgiveness are two elements in a single social circuit. There is a need, therefore, for the required response to be offered so that the circuit is completed.
I think that is what Bob meant when he said the bird “needed to be flipped.” Bob had said something to which being flipped off—in an affirming and collegial way—was the appropriate response in the same sense that accepting a public apology is the appropriate response. There is, here, a two-action circuit. Bob did the first part by saying something provocative or outrageous or whatever it was he said. Somebody needed to do the second part and an unexpected person stepped up and did it. 
So Bob was not “left hanging” because someone…finally…took the other predefined action. This person is, in fact, not a prominent bird-flipper. I have never seen it from this person, despite having many opportunities. But this person surveyed the gathering, looking for someone who would do what needed to be done, and finding no one, did it as a social grace. A necessary fulfillment of the social circuit.
And that is what Bob meant when he said that the bird “needed to be flipped.”
Finally, I want to note that this is the kind of post I had in mind when I started this blog nearly 10 years ago and why I called it “the dilettante’s dilemma.” I had just learned that “dilettante” is a word derived from the Latin delectare, to “allure, delight, charm, or please” and that is a freqentative of delicere, which has the same meaning. 
 This is a very congenial group, so it does make sense for an offense to be “achieved,” if it is just the right offense in just the right amount.
 Flipping the bird can be effectively alluded to as well as effective done. President Carter, the prominently Baptist president, observed, in the second years of his presidency, that he seemed to be settling into Washington. People are beginning to wave to him, he said, “using all their fingers.” He meant, “rather than just that one.”
 This same sense of calling for a response shows up in Remember the Titans where Ronnie Bass (Kip Pardue) a new white guy in a team of mostly black guys, makes a remark and holds his palm out to be slapped in affirmation. The black guys, who would have done this automatically to one of their own, are taken aback and no one responds quickly. Ronnie says, “Come on, bro. Don’t leave me hanging.” The “leave me hanging” captures exactly why there are times when the bird needs to be flipped.
 Frequentatives are common in English. It is just not common to point them out. “Sparkle” is a frequentative form of “spark.” How cool is that!