Why does my best friend's ex hate me?

Well,one of my best friends,*Pattie,had a boyfriend,*Robert,who I never personally liked.He used to be nice to me,by constantly calling me,but I found out that he was using me so he could get in contact with my best friend,since this was before they started to go out.In my eyes,Robert is one of the most inconsiderate people,I've ever met in my life,to be honest with you.He was very mean,and to this day,still is,to me,but then again,I realized that he was like that to most of Pattie's friends.
At most parts,Pattie was basically brainwashed by Robert to do this,do that and so forth,when most of the time,she wasn't confortable with it.When they finally did,break up,she was free and moved on with her life by getting a new boyfriend,who treats her well.
Well,tonight,I was at Homecoming,and every time I would pass Robert,he would be like, 'Ewww,I'm blind!' to me!I didn't say a word to him,and he still did it,out of nowhere.What is his problem?Should I confront him about this,or ignore the fact?

His behavior is very immature and irritating. If you didn't like him to begin with, then don't concern yourself with his actions. If it gets to a point where you absolutely cannot stand it, straight up tell him that he needs to stop.