For those that don't know, or only have heard "senpai" in passing, the term basically means "senior" but it refers to senior classmates, coworkers, etc. The thing is that in Japan, it's common as a name ending like -san or -kun, and you also use it to address your seniors to their face.  For better or worse... we just don't have a term we use like that in English.  So who knows... maybe it'll get imported one day as a word in our vocabulary outside of a joke? Like some sort of lingual weeb-pocalypse.