When you try to "pretend" like hit someone you make a sound '팍!' with your mouth. and when you are annoying you make a sound '씨!' So normally you can "what are you looking at? 뭘봐? 팍! 씨!" 씨 is more usual to say when you get annoying like 아 ~씨! 짜증나 something like that but '팍' is fun way to say when you are pretending to hit someone. and there is a some typical gesture with this word.... but hard to explain in words haha anyway 팍! 씨! is fun way to express I think I was not so sure if this was what you meant but saw the link you added and yes I think this is what you meant

Well 씨 is like Mr, Mrs, etc... Maybe 팍 is a nickname (2Pac fan?). 팍씨 isn't an actual word, I can tell you that much.

There's also a image with the same word on it. http://social.phinf.naver.net/20130901_136/1378046981552EuIFe_PNG/Screenshot_2013-08-06-21-14-07.png?type=w320_1

Hmm... I saw it on another person's Kakao talk status, and there's only this word.... So...

It might help to include context. What sentence was it used in? Where did you see or hear it?