Replying to 12 items or less lane how do they work?!!?

I was at the store today, getting two 2 liter bottles of Fresca. So I see a Express Lane, like most people with hardly any items at least you would think, I go to the lane only to be stuck behind like 3 people with a quite a bit more then 12 items. Then some lady comes behind me and slapped all her items on the belt, takes like half of the belt and the mass of items is like half a foot tall. Whats the point of having an express lane is nobody even uses it as one. It's not that hard of a concept to grasp.

Anybody have similar experiences? It's not like you can say anything cause then you end up looking like an asshole, is there anyway you can seem polite and still tell someone "oh this is a 12 item express lane, can't you read"?