Why do guys act like this?

He is 25 years old. No matter how nice I am to him (we have mutual friends) its always followed with "I hate you!" Or "eff' you!" Or "shut the 'eff up!" I'm not sure how to deal with him. My friend says he's naturally just a mean person and that I should ignore him, but I can't help defending myself. I just want to better understand what in god's name is his problem. I can't really avoid him, but I'm not gonna sit there and let him insult me for no reason. Help?