A physical attack requires a physical response. Words are just words, they bother us because we allow them too. They pose no physical threat. There is enough violence in the world. Don't let someones words cause you to make a mistake you wish you could take back.
Gregg... I'm gonna kill you.
Just words or a real threat ?
Over the internet they might mean very little however, face to face, if you considered my intent be real, then you'd be within your rights here in the UK to physically defend yourself, even though to that point, you haven't be physically assaulted.
Walking way in those circumstances just might not be the right thing to do if the person issuing the threat actually means what he/she says.