1.) A condom.
2.) More specifically, a condom that has been inflated (usu. by mouth) and tied, thus becoming a balloon.
"We got a fuckballoon from the library bathroom dispenser, inflated it, and tossed it around in the street until, when Nik tried to catch it, it popped. He declared, loudly, that he'd just gotten the whole world pregnant."
"Sometimes I think Nik uses his skull to store used fuckballons in."