I wouldn't. I would rather the person/people be surprised, but also incase you get a less than enthusiastic CM, they won't let that ruin their experience.
If your Dad is a ham, he'll probably give it right back to them and be the life of the table! It's all in good fun, I'd keep mum and let them experience it for themselves!
I've never seen anyone run out of the restaurant in embarassement!
I wouldn't. I would rather the person/people be surprised, but also incase you get a less than enthusiastic CM, they won't let that ruin their experience.