Coupons can be used on regular priced items ONLY. If an item is on sale or there is a site wide sale happening (i.e Black Friday) coupons CAN'T be used.
If you have a regular price item and a sell item in your cart the coupon will only come off of the regular priced item.
This applies to ALL coupon codes including but not limited to forever codes for existing customers.
The ONLY exception is for the codes generated from the loyalty program. You CAN still use your points for those discounts and free shipping.