To put a really legal slant on it. If the neighbour died, and the beekeeper was sued, he's been plainly negligent. The admission of guilt implied by having to buy a neighbour a veil, implies he knows only too well, that the bees are stinging him, in his garden. Out of interest, if you are a BBKA member you are not covered if negligent, so you might want to consider very carefully how you choose to manage the situation.
Having a record that you moved an aggressive hive away is a good defence, should another bee from another colony sting them. Having the defence "I gave him a veil", to protect him from my vicious bees that I didn't want to move has disaster written all over it, and a lawyer for the poor chaps family would be rubbing his hands together with glee.
Like a recent poster, for your own enjoyment, surely nasty colonies need sorting out (e.g. moving out until resolved). For your peace of mind, it needs sorting out, and for his good health, future neighbour relations and as a representative of all us as beekeepers, you need to sort it out.
Regards,
Adam