Help me understand this excerpt from "Great Expectations"

Can some one help me understand this part? I have absolutely no idea how to make any head or tail out of it. This is a part of "Great Expectations":


"Casting my eyes along the street at a certain point in my progress, I beheld Trabb's boy approaching, lashing himself with an empty blue bag. Deeming that a serene and unconscious contemplation of him would best beseem me, and would be most likely to quell his evil mind, I advanced with that expression of countenance, and was rather congratulating myself on my success, when suddenly the knees of Trabb's boy smote together, his hair uprose, his cap fell off, he trembled violently in every limb, staggered out into the road, and crying to the populace, "Hold me! I'm so frightened!" feigned to be in a paroxysm of terror and contrition, occasioned by the dignity of my appearance."

(Not a Teacher)

As Trabb's son, who's hitting himself with a blue bag, approaches, the main character decides to keep a calm, unperturbed look on his face as he passes him. When they get close, however, the boy pretends to be afraid of him and jumps out into the middle of the street to make a scene.

Note: I've never read Great Expectations, so I can't offer too much insight into what's going on here. The kid sounds like an obstreperous brat, though.