My biggest pet peeve is unsolicited advice. Don't tell me how to feel; don't tell me what I "should" do, don't try to fix me. Just...don't. I'm a grown-up. If I want advice, I will ask for it.
When I tell you how I feel (tired, sad, stuffed up, frustrated, etc.) please do not tell me how to fix it. Do not say, "Oh, have you tried vitamins?" or "Maybe you should see a therapist" or "Why don't you drink some green tea."
If I tell you I burned my brownies, don't tell me to try a different pan. If I mention that I'm frustrated because the CTA is running so slow, don't suggest that I take Metra. I swear, the next time someone gives me unsolicited advice, I will scream.
Unsolicited advice-giving has reached epidemic proportions in this country, and I think it's time we all take a stand against it.