.crossing lines.

There's this older man that I know that has crossed a line and makes it me feel super uncomfortable. I don't know how to address the problem without going off. I really want to tell my Dad to step to him. I'm older now and I need to handle this on my own but things like this make me want to run to someone who can protect me. I want someone to handle the situation but there isn't anyone there to do it. How would you handle it? I'm just not use that my warning will be enough. :-/