Well, I recently had a conversation where I realized that just about
anything sold in a supermarket could be used to kill someone if they were
tied down, so danger is definitely a relative concept. Going by total
numbers of people killed, if you arrived in a car, or with a pack of
cigarettes, you would have two of the most deadly common objects around.
However, while technically correct, bringing these two items would not win
you many party points... :-)
If you went to a hardware store and bought a nice vicious looking axe, or
rock pick, that might do the trick. Or perhaps you could wear a necklace
of garlic and bring a large wooden stake. Of course, this might not help
you attract women at the party...
Maybe you could do some parlor chemistry, bringing some flash powder, or
similar. You won't win the prize, but it'll definitely be an
attention-grabber (and who cares about the stupid prize if you have a
couple phone numbers at the end of the night?)
Hmm, perhaps a burning cigarette combined with liquid oxygen....