Who taught: Jake and Patrick? Oh and Phil (Phil told me it is important to give strong and long accent to “bull”)

Maybe I should not add these kind of expressions here but I guess it is still useful in a sense that at least I can understand what it means when other people say it.

So, simply, BS is an abbreviation of “Bull Shit.” So if anyone say something you think totally nonsense, you may use this expression but I guess you do not want to use it to somebody you just met unless you do not even care about them (????).

Well, not really recommended, though.