A form of mental illness. Symptoms include the tendancy to throw a massive tantrum about the smallest of things, a need to have everything his/her way, and an inability to form friendships with other human beings.
Never trust someone suffering from Rentapest Syndrome, they will inevitably attempt to stab you in the back. Fortunately, someone suffering from this illness is also very stupid, and are more likely to kill themselves than anyone else.
Man: "Here Mr Brown, let me give you a million dollars"
Rentapest Syndrome sufferer: "Get the fuck away from me! These dollar bills are all creased you fuck! I hate you!"