"Lock the doors and close the blinds -- we're going for a ride..."

Hypothetical question for you all: (And if you know what I'm getting at, please don't spoil it for the rest of the folks quite yet.)

You work at a "food cooperative" at your local university -- housed on campus property. It's been a staple of the university for decades now -- the only real place on campus where you can get truly organic food -- much of it far healthier than the junk they serve in the dining hall. But the best part is that this is a true co-op -- profits are used specifically to pay operating expenses, including the wages of the employees.  There's no management; everyone who works there has an equal stake in the co-op -- which really isn't a financial stake as much as one of decision-making.

You're at the cash register during lunch.  People are coming and going with their assorted foodstuffs. One person comes up to you to pay for his/her items.  As you're about to ring him/her up, you see that s/he is wearing a t-shirt which you deem to be offensive.  Depending on your own beliefs, it could be:

I STAND WITH SATAN.

JESUS CHRIST DIED FOR YOUR SINS.

BUSH LIED, PEOPLE DIED.

I STAND WITH KIM JONG IL.

AMERICA - LOVE IT OR LEAVE IT.

HITLER WAS A VEGETARIAN.

Anyway -- it's something like that -- something which touches a nerve.  The customer is not being belligerent or even speaking during the whole ordeal.

What do you do?

Do you serve the customer without commenting on the shirt?
Do you serve the customer and get into a disagreement about the ideology of the shirt?
Do you refuse service to the customer?
Do you kick the customer out of the store?

Just curious about what you feel would be an acceptable response in a situation like this...