@Matanui606 While BS is only considered an expletive due to the second word that composes it, that second word, which is rather crude to humans to say in many contexts, is only so because we have developed a cultural revulsion to our 'excrement'. Matoran, having no similar function, would probably not have an equivalent phrase or word. It developed due to our revulsion of the stuff, however in context, we tend to use it to represent anger or frustration instead of revulsion, and thus I find 'BS' to be relatively unhelpful in determining a cultural equivalent.
@ToaKhrazix Yeah, Piraka was probably the worst word we know of that you could call a Matoran. Spiriah and Roodaka, on the other hand, while synonymous with those words, were not actual expletives to my knowledge
@Ulti Maybe part-beast meant barbarian or uncivilized? Matoran placed high esteem on civility. On another note, I can't remember anyone saying Glitch as an expletive.
Also, I remember Reidak uttering a 'long line of curses' after getting tossed off the boat by Avak or Vezok on their search for the kanohi dragon. In Legacy of Evil, I believe.