Why is my friend acting like such a jerk? He has a girlfriend anyway!?

I was in a room talking to a co-worker (who's a guy) and my friend came in. He sat far away from me and co-worker. He kept interrupting us with stupid questions like "what day is it today" Then he started joking on me and subtly insulting me so I joked back with him. After about 10 mins of talking to my co-worker I decided to leave so I said bye to both of them, & then my friend just came out of nowhere insulting me again about my job. So I got all defensive and then he started insulting this other guy I liked. He basically just went crazy on me just when I was going to leave. I was so mad at him & he caught me off guard. It was like he's tryin to get a rise out of me! The odd thing was last week I showed him a picture of my ex cause I thought he looked liked this guy I wanted to date (he didn't know it was my ex's pic) & he started going crazy asking me questions like why? do you like this guy? why don't you just date him then? are you in love with him? why don't you just marry him!