I love your question and I am going to answer this question with all sincerity. Sometimes, its pretty tough getting over your ex because you are so smitten by them that you turn your blind eye to signs she exhibit during the relationship.You never saw it coming..you just got that call from your girl and the first thing she says is "its over"..it would definitely be surreal.
In this case,you try every means to get her attention..you call her severally.. You send a flood of text messages.. you stalk her on every social media their is..you even travel across the ocean just to mend the relationship.. then you go on your knees like a fool..just to get back together with her.If you are lucky to be in the same room with her ,definitely that person will try every means possible to get her attention.
Back to your question, if I'm to be in the same room with my ex,I will just say a normal "hi" and make her invisible. She is my ex for a reason. Everything that happened between us was in the past..and we have both moved on.Its just childish to try to get her attention..