First of all, portals work on any flat surface, it has to be a special surface for it not to work. Secondly, you couldn't really put a portal on yourself due to size problems and the fact that you're probably not flat.
However, assuming that you could place a portal on yourself, in which case you're probably some sort of man behemoth, you could stick you limbs through, and even your body. The portal would be the only thing the couldn't go through, and even if you did attempt it the portal would probably either be impossible to force into the other, or it would automatically shut down, severing your limbs if they were already inside the portal.
As far as I'm concerned, no universal implosion, but you would have to move the portal on you to a different location in order to actually get your whole body through the portal. And for those of you thinking that moving a portal to another location while you're still in it would kill you obviously haven't tried it in-game, what it does is spontaneously teleport the part of you body sticking out of the moved portal to the portal's new location. Not quite sure how that works even in-universe, but that's what happens.
EDIT: Either that or the portal doesn't move, it's been a while since I tried it. In this case you'd simply be unable to actually get your whole body through the portal and be forced to withdraw yourself and move the you-mounted portal.
END EDIT
Out.