+1000!

I can see going a little over, especially if the items are small and quickly scannable, but the people with the mounded cartload of stuff really take the cake!
A coworker of mine once had a customer innocently say "I have a few more than15, is that okay?" She said sure and went back to checking the two people ahead of the woman.

Then she looked up.

The woman was unloading an entire cartload of groceries onto the belt. She had over 50 items.

My coworker called her on it, and the woman whined, "but I'm in a hurry!"

My coworker said "So are all the people behind you!"

She made put all her items back in the cart and go to the appropiate line.