Originally Posted by akl_traveller

One can both (a) not suffer fools and (b) still remain polite.

Here's a hint: "This bill is wrong" vs. "I should think you might have accidentally mixed up my order - could you check?"
Both lead to you getting your money back. The latter one enables you both to save face (you if you got it wrong, them if they made a mistake."

Here's how you could (a) not suffer fools and (b) be polite.
"Might I borrow a pen?"
"Absolutely," (smiling) "I always think it's a good idea to have a pen, you never know who might ask for one!"

The recipient will understand exactly what you are saying, but you are doing it in a polite manner that leaves everyone feeling happy.