What does “two-bit (jerk)” mean?

"Two-bit" is an idiom meaning cheap or petty. It comes from a slang term for the American eighth of a dollar, a "bit." Even after the "bit" was phased out of the currency in 1792, the term "two-bit" persisted to refer to the quarter dollar.

A two-bit person isn't worth much. From the Oxford English Dictionary under "two, adj, n., and adv.":

1978 T. Willis Buckingham Palace Connection viii. 155 Some other two-bit General will try shooting us up.

When applied to people or things, unless it is used ironically, it is a put-down or insult, implying cheapness or low quality.

So "two-bit jerk" may mean that the character isn't of much importance and he's a jerk (i.e. he's rude or crass).