These are amazing boxers and this is a bit of a hack.
So enter one pair, then click proceed to checkout. A popup appears saying add an emergency pair for $20, click agree and then click the X to remove popup, then click checkout again, repeat until you have 7 pairs. Now you will be charged $84 total, now on the check out page enter code Waist20.
@pirlo thanks 15 pairs for $78, change the emergency pair quantity to 14 and check out.