Without hurting his feelings

I was at lunch one day with one of my friends when i looked over and saw a guy who i found out was Meatally retarted.My friend started laughing so i told her she shouldnt judge because god is going to end up punishing her one way or another.Anyway,it was 5 minites later when she started laughing and said he was starring at my chest and i looked over and he was!I guess he didnt know i was looking but when he looked up he started smiling and went back to the same thing when i got up to go dumo my tray i looked over and saw him scooting touching the seat i sat in when he saw me coming back he moved.When it was time to go one of my friends caught up and said she saw the dude looking at me and she said he did the same thing to her but instead he followed her around and it wasnt recently that he stopped.I dont know what to do this has been going on for 2 days now.