The origin of this word is southern asian, but it can relate to several lantin terms. Basically, it means that you are annoying, nauziating or god damn irritating.
A person who is smart but all the time seems stupid. Constantly smoking weed, drinking beer, and sword fighting, and sometimes putting one's head through the wall, a pusak likes to do all things fun, even dumb ones. Many people may seem like a pusak, but in the end there are very few.
Oh man, last night at the party Marky put his head through the wall when he was hammered. WHAT A PUSAK!