“I appreciate you” is a polite of way of expressing your disgust with a particular object, situation or person. When utilized in this format, you leave the subject of your statement wondering why you were so polite when in reality you were simply telling them to fu*k off.
Boss: "What's wrong with you? Your results are horrible." Employee: "Thank you, I appreciate you."
Unkind Person: "You wear a 4x shirt, seriously?" Victim: 'Yes I do, I have a gland problem. I appreciate you."