Explain Gene’s reaction to Leper’s accusations?

One thing that Leper is able to do after his army experience is peg Gene's personality, and know what he did to Finny. Finally, naïve little Leper evaluates Gene in a more accurate way than anyone else in the book; "You always were a savage underneath," Leper tells Gene, "a swell guy, except when the chips were down" (136). The appraisal is absolutely right on, though Gene of course doesn't want to hear it. So Gene breaks out into violence, confirming Leper's statement.Gene is unstable and unpredictable when faced with the truth, or with something that upsets him; he's not quite the nice rule-abider he wants to portray himself as, as he displays once again.