Aldous Huxley introduces the idea of the "victim-friend" in Chapter XII, as Bernard muses on the role of John, who "as a victim, the Savage possessed, for Bernard, this enormous superiority;" mostly because John is available for him to pick on (182). 

To Bernard, the victim-friend is someone that he can unapologetically use.  He values John as a friend for his allure as a 'savage,' someone he can use for entertainment at dinner parties to impress the Arch-Community-Songster with.  Bernard wants someone that in a friendship type role that he can be a little mean or petty to, without having to suffer the consequences of that particular behavior if he acted that way with someone important or meaningful. 

"One of the principal functions of a friend is to suffer the punishments that we should like, but are unable, to inflict upon our enemies" (182).

Bernard's view of the 'victim-friend' reveals his petty nature and selfish, mean-spirited attitude.

What is a "victim-friend" in Aldous Huxley's Brave New World?

This term is taken from Chapter 12 of "Brave New World" in which John the Savage is described,

As a victim, the savage possessed for Bernard, this enormous superiority over the others: that he was accessible....Bernard's other victim-friend was Helmholtz.  When, discomfited, he came once more to ask for the friendship which, in his prosperity, he had not thought it worth his while to preserve.

On the day after John foils Bernard's plan to exploit him, John is sympathetic to Bernard, but he says he preferred Bernard when he was unhappy rather than happy being a sham.  In anger, Bernard lashes back at John, blaming John for the troubles he has suffered the night before.  Thus, John is both friend and victim.  Likewise, Helmhotz is both friend and victim as he provides Bernard solice when Bernard wanders back to him, offering his friendship without reproach as though he has forgotten any umbrage.  Yet, Bernard turns on him,too.

Bernard was duly grateful (It was an enormous comfort to have his friend again) and also duly resentful (It would be pleasure to take some revenge on Helmholtz for his generosity.)

That Bernard treats both Helmholtz and John as both friends and victims indicates that he himself fails as a person of integrity; instead he is shallow and uninteresting on his own.  However, he does arrive at some maturity at the end as he realizes that he has accepted contentment over truth and accepts his exile to the Falkland Islands as he realizes that as Mustapha Mond has said, he is

being sent to a place where he'll meet the most interesting set of men and women to be found anywhere in the world.

At least, on the islands, Bernard can find true friendship and not have to exploit others, making them victim-friends.