Want to use a coupon after the expiration date? Just berate the cashier!

If you come into the store with will and determination to argue your cashier into submission, you will always get them to give up and apply the discount! Personal attacks are encouraged, as it breaks the will of the cashier quicker. I've seen it successfully work a few times today with minimal lasting damage.

The only thing you have to lose is self-respect, but who needs that anyways?