I've had this very discussion with co-workers at several jobs. They all thought I was being pedantic when I said that you never put anything that might be offensive to a customer anywhere in the code. and that you should assume that the customer is the world's biggest prude when deciding what can offend.
They always responded "But the customer will never see the source code"
To which I was answer, "You hope they won't, but you can never be sure."

Boy do I feel vindicated today!

I've been on projects where I have removed comments in which programmers said rude things about the customer- by name (and put their initials at the top of the comment, apparently so that management would know who to fire).

When it comes to clients, you can never be too careful.