The evil God argument is a common appeal to emotion fallacy made by atheists to attempt to disprove the Bible. They find a shocking, usually out of context verse/passage and use it to say "therefore, God doesn't exist." The problem with this argument, aside from the fact it is usually based on out of context verses (Luke 19:27 being an excellent example), is that the argument is both emotional and circular.
It is circular because morality is inherently tied to whether or not the Bible is true. If the Bible is true, God is the ultimate source of morality, and thus cannot be evil, period. Thus, in order to prove God's immorality, you must assume He doesn't exist in the first place, which is the very point you're trying to prove!
It's emotional because it doesn't really prove God doesn't exist so much as convince people that they don't want Him to. If, for sake of argument, there was some kind of higher authority to which God could be held accountable, and He actively disobeyed that authority, that wouldn't make Him cease to exist. That would make Him evil.
But as it stands, God has no higher power to answer to. The universe, and everything therein, was created by Him, for Him. It's His. He owns it. He can literally do whatever He likes with it, and us, and we have no grounds to criticise Him for it. Thus, really, when an atheist uses the "evil God" argument, they are actually claiming that they are the higher authority.
Does this not sound familiar? It's the very goal Satan had (Isaiah 14:14), and the lie with which Satan deceived Eve (Genesis 3:5). God's authority, and God's power, are both things we, as humans, crave. But it's not for us. God's authority belongs to God alone, and all attempts to usurp it are called "sin". Ironically, a lot of the things atheists use to call God evil are the punishments for sin.
But while we do deserve those punishments for trying to usurp the authority of God, we do have this blessing: God doesn't want to punish us for it. Instead, beyond all imagination, God sent Jesus to live a perfect life as a man, dying on our behalf and rising again, so that we, too, may have eternal life. Rebellion made us worthy of punishment, but if we, in faith, submit ourselves once again to the authority of God, we can be forgiven.