I'm a DIYer with an embarrassing quantity of flavorings, and I still get bored regularly. When I do, I go for plain, strong, flavors like peppermint, red-hots cinnamon, or licorice/anise. Sometimes plain apple will do, too. Occasionally I just quit the flavors and vape unflavored base a while. By the next day, I'm usually ready for my usual fancy coffee and bakery flavors, so I make sure they're at the ready.