Mr. Gilmer, the lead prosecutor against Tom Robinson in Harper Lee's novel To Kill a Mockingbird, constantly refers to Tom Robinson as "boy." All of the following dialogue is taken form chapter nineteen where Mr. Glimer is questioning Tom Robinson.
"Had your eye on her a long time, hadn’t you, boy?"
“Then you were mighty polite to do all that chopping and hauling for her, weren’t you, boy?”
“With Mr. Ewell and seven children on the place, boy?”
“You did all this chopping and work from sheer goodness, boy?”
Here, one can see, in question after question, Mr. Gilmer refers to Tom Robinson as "boy." Mr. Gilmer does this for two reasons.
First, by calling Tom a "boy," Mr. Gilmer is lowering Tom's status. Tom Robinson is a man, not a boy. The fact that he keeps referring to Tom as a boy lessens Tom.
Second, when one refers to another as a boy, they are showing that they have power over them (if it is an adult speaking to another adult). Mr. Gilmer wants Tom to fear him, and by calling him a "boy," Mr. Gilmer is showing his power over Tom.
In regards to technique, this is simply a verbal attempt to control another person. In regards to literature, this does not have a term by which it is called.
Is he not trying to belittle Tom Robinson, by calling him boy is he not trying to show that Tom is beneath everyone else there. I'm not sure if that is a technique tho, sorry.