The worst thing i can do to someone who has been dumped.

I can say a lot of things to someone who is dumped. One of those things will be to laugh and point at him for being dumped. This will not only make others know about the situation but will make the person more sad. I can also ignore the person and listen to the one who dumped him or her and agree with them just to make the person feel alone. I think this would be more than enough and would make the person feel angry and stupid.