Japanese; I've heard that it's rude not to use suffixes after someone's name, but Sai (Naruto) says that...

The use of a name without a suffix is normally used when the two people are really close often it's used with lovers or really close friends. I'm not sure how factual this is but I've read that using a name without a suffix can be translated to "My Sai" or whatever the name is. Not using a suffix with someone you just met or aren't very close to can be considered rude so in a way both are correct.