What's up with my dads friend?

My dads friend is creepy he stares at me when I walk down the street and one time I was in my house I had my pajama shorts one ( witch are really short :p) and a aeropastle tank top and had a throw blanket and my butt was not covered with the blanket and he kept staring at me this was while my dad was upstairs changing I don't know what to do cause my dad won't believe me and I can't tell my mom because I don't have one I just want to know what's up with my dads friend?