They love to see others quail before them, as they themselves would be ready to quail before those they hold in awe; and it is no small set-off against their own terrors to feel themselves in turn objects of terror to others.
People of this sort are of course generally cowards and toadies, and in bullying they find the fullest gratification of their craving for power.
Bob may sometimes feel a passing pity for the poor little wretch he is tormenting; but until that poor little wretch consents to knuckle under, to apologise, to obey, to accuse himself, in the manner Bob selects, he must not be spared.
Boys who want to understand what real bullying is, should call to mind that parable about the servant who, having quailed and cringed and implored before his lord until he was forgiven his huge debt, forthwith pounced on a poor fellow-servant who happened to owe him a few shillings, and, deaf to the very entreaties which he himself had but a minute before used, haled him off to gaol till the last farthing should be paid.
He was bad enough; but the wolf in Aesop's fable was still worse.

The poor lamb there owed nothing; it only chanced to be drinking of the same stream.
"What do you mean by polluting my water ?" growls the wolf.
"I am drinking lower down than you," replies the innocent, "and so that cannot be." "Never mind, you called me names a year ago." "Please, sir, a year ago I wasn't born." "Well, then, it was your father, and it's all the same thing; and, what's more, you need not think I'm going to be done out of my breakfast by your talk--so here goes!" And we all know what became of the poor lamb.

A gentleman cannot be a bully, and a bully cannot be a gentleman.
By gentleman I mean not the vulgar use of the word.

The rich snob who keeps his carriages, and counts his income with five or six figures, and considers that sufficient title to the name, may be, and often is, a bully.

His servants may lead the lives of dogs, his tradesmen dread the sound of his voice, and his dependants shake in their shoes before him.
But a gentleman--a man (or boy) of honour, kindliness, modesty, and sense--could no more be a bully than black could be white.
Bullying is essentially vulgar, and stamps the person who indulges in it as ill-conditioned and stupid.