What do you do when someone you despise asks to be friends on Facebook?

The husband of an old friend is an absolutely horrible man. He is the reason I never looked up this old friend on Facebook. Alas, she found me and asked to be friends. Then her sister asked to be friends.

Then, yuck, today her husband asked to be friends. So if I say no or ignore him, she will know it.

I was thinking of friending him, and then quietly unfriending him in two weeks or so. What do you think?

Have others faced this dilemma?