Yes, very tricky stuff.
I was in an argument with someone a couple nights ago. Well, less of an argument and more of a freeze out. When I expressed that I was "not pleased," and shared my reasons for why, this person said, "You're right. And I regret that." And even thought I'd spent the last few hours internally fuming over the situation, I was over it within ten minutes. All it took was them agreeing with me and expressing the same sentiment I felt.
Try it with your character. Have your MC recognize their unreliable tendencies and dislike them just as much as the other characters. Maybe show them trying to change. That can go a long way with a reader.
I used to meet with a group of women every Wednesday morning. And every Wednesday my friend Amy was late. And during our study time, her cell phone often rang because she forgot to turn it off. With a person I didn't like, these things would've driven me crazy. But I loved Amy, so they became funny little pieces of her character.
So something else you can do is make your character extra lovable. So lovable your reader doesn't want to be mad at them for being unreliable.
Hope this helps.
Have a writing question? E-mail me.