싸가지 is a term you will hear a lot on drama series. basically reserved for someone who has no manner... unpolished, unruly.
another term you might come across is 버릇없는/버르장머리없는
놈 is a common term for guy. (not really used in polite company but perfectly ok to use among close friends)
In any case, 싸기지 is probably not well advised to direct at someone you don't know well and especially when you do not know what the cultural norm of dictating such use.