Nothing. I wouldn't have the person in my home or talk to them or otherwise acknowledge their existence (unless, for some reason, I could sue him/her and destroy his/her life). Food revenge isn't something I'd do. I suppose if the person were truly about to die from starvation I would not him/her die (under most circumstances).
There are ways people can causes harm/damage without physically harming them. To me, it would be worth looking at the person in court (for as long as it took) to be able to hurt them through the legal system. I wouldn't try to sue someone for some little thing, but if they did damage to me or my children I'd sue them as quick as look at them.
OK all you Miss America wanna-bes...here's an honest answer for ya. If I had one of those 9/11 terrorists in my kitchen, I would be serving them up a nice helping of their own brains with some Fava beans and a nice Chianti...
If they're an enemy, the must have done something terrible. I'm talking about killing my family, sexually abusing my kids, something like that. In that case I'm not quite sure what I'd do, but my vengeance would echo down the years. I'd go mad and parents would use my story to scare their children for a thousand years.