Can I tell God that I'm disappointed or angry with him?

Yes—and Scripture itself models exactly this kind of honesty, rather than a polished, edited version of prayer.

Job, in real anguish, says to God, "I am disgusted with my life. I will give vent to my complaint and speak in the bitterness of my soul" (Job 10:1). That's not a private thought Job later apologizes for—it's part of a book the Bible holds up as faithful, even though Job never gets a full explanation for his suffering.

You don't need polished, careful words to talk to God. "I'm angry." "I don't understand why you let this happen." "I feel let down." These are prayers too, not failures of faith.

What matters is staying in the conversation rather than going silent. God can handle honesty better than performance—and a relationship where you can only say the acceptable things isn't really a relationship at all.