Yeah, if you tell your friends your a ninja and do something cool, you'll have a pretty good chance to get through it and not have them really think about you being a trained assassin. If you tell them after you pull out a sword and attack someone out of the blue and they see you standing over the bleeding body, you're going to get the Gross Pointe Blank reaction.
Not sure how this plays into Youko. She's drinking blood, so the only thing going on with her is the vampire traits are getting stronger (invisible to photographs, which kicked this arc off... though why that effects the sunscreen & clothes...).