Is this a good idea to start back a friendship with my ex? (pointers)?

We sit by each other but we don’t talk we use to but not anymore it was because I said stuff to him, well 4 or 5 months pasted and we still haven’t spoken to each other but he has said stuff and randomly out loud for me to hear that is to me to get my attention but I just give him the cold shoulder and not react but now I want to say something but its kind of hard cause we haven’t spoken for a while now and it will feel awkward for me to say hi, cause he could be thinking what the hell why you saying hi to me. Should I just turn to him and say oi or hey then smile and look away? We have this thing we look at each other smile and look away but that was ages ago we did it cause it felt like we were playing a game or playing around it was something cute and sweet . so should say oi smile and look away?