There is an awesome free app that can help and a paid one that shoehorns the missing functionality when you really need some doubles négations, but I wonder when will we be able to do this: Exclude Collection(s) from Discount Coupons?
You have us here as well. Very much like "Or" functionality for smart collections, we're chasing down the ability to have exclusion rules allowed for our discount engines, too.
Talk to you soon!
Matthew ButtlerGuruShopify Inc.