It's not that I do not understand, rather I refuse to jump to a conclusion based upon an assumption.dude why dont u understand that he was pretending to be someone else and goofing off with them just so he can delay them(not to mention why did his personalty change as soon as zetsu arrived why not earlier it cant just a coincidence)
You are assuming that he was just playing or pretending to be someone else, which to your credit makes sense, but there is no data to confirm or dispute this claim. All we know for sure is that at times he displays a goofy personality, and at other times he display's a serious personality.
Likewise, there is no data to confirm Bahamut's hypothesis that he has a split personality. Either of these could be true. Simply because you believe that he was pretending to be someone else, it does not make it a fact.