How do you kill an angel?

Actually, while an angel is in mortal form on earth, they can be affected by one thing: qeres. The Egyptians had a perfume called qeres that was used during mummification to provide the first 'sweet breathe' of the afterlife. Qeres is extremely rare substance because its recipe has been lost, but small amounts still exsist. this perfume is a lethal poison to an angel (fallen or otherwise), and if poured over, say, the blade of a knife, could in fact terminate an angel. While non-lethal to humans, it can burn or poison anyone who carries the Nephilitic gene. (see Genesis 6). If you are still thinking that all Nephilim died in the flood, think about Goliath, or King David's "men of great reknown". But yes, qeres can kill an angel. And no afterlife awaits them either. This isn't some role-playing B.S. or T.V. show, this is legit. Go ask your local Catholic priest if he knows what the 'Hashilim project' is, or the real reason Jews (who are the most dominant carriers of the Nephilitic gene) were exterminated. Or why most children born with synaethesia carry the gene. Or why Mengele expirimented on Hebrew twins. You may not get answers, but you will be asking the right questions...

I think the original answerer misunderstood the question, or just rather ran off on an tangent unrelated. Killing an Angel is really something that I would not recommend unless you want the wrath of God unleashed on you. The rest of the original answers, well, have fun with that.

the wrath of god is a joke Christians say to make them feel important and better than everyone else and also I'd like to remind everyone that a god has special rules that prevents them from harming a full human

I think much of the above is well-intentioned junk. One guy feels that a magic potion will certainly kill angels but is harmless to humans, though no one has done it or no evidence is supplied. Another guy thinks gods have rules about killing humans. What about the Great Flood, the Egyptian plagues, the Egyptrian Army pursuing the Israelites, or Sodom & Gomorrah? Rules, indeed!