any good way to say goodbye to someone you hate, when they're leaving a job?

Except now I’m just wondering what he/she actually said?

Yup. After that, you can go home and talk about how glad you are the douchecanoe is gone.

Bonus – you can later use the interaction to answer a stupid interview question about “tell me about a time when you had to work with someone you disliked…”

Dilbert got it right in 1994: PHB: “Tim will be leaving the company to pursue other opportunities. Note the absence of key phrases such as ‘we regret’ or ‘years of dedicated service’. And notice that his new opportunity is not described as ‘exciting’”.

Dilbert: “I think you’re reading a little too much into that announcement.”

PHB: “No, I’m reading the footnote.”