the third person is protected by law due to kakashi's innappropriate sexual conduct against her.
Charlie Brown:I gotta rock...
Kakashi:I Gotta Uchiha BIYATCH!!! Now What in ya face !!
Gai: Turtle timee gangstaaaazzzzz
But senpai doesn't means teacher, does it ? :S
You could think of it this way, you are a newcomer on a team (of some sort). The captain of that team (or anyone that's been around relatively longer than you) would be your senpai. Sensei (teacher as we all know, i think) would be the coach.