The cover needs to say Christmas loudly, and be skeptical of Christmas without being darkly skeptical. The book is more like A Christmas Carol with a very religious view of Christmas than Santa or secular Christmas like "A Christmas Story," or "Elf." It's about a conversion experience around the Christmas Holidays. It's not about reindeer, elves or snowmen. These symbols are okay to use in a playful way, however. The Christmas imagery should be clean. The word "Friggin'" juxtaposed with happy Christmas images is likely enough, though you might add something a little edgier around that word.
I'm not an artist, at all. My limited vision is a lot of red, white, and green, the title "Merry Friggin' Christmas" in big letters taking up at least half the cover in Christmas motifs, likely hand drawn rather than a standard font (or, at least, significantly manipulated and made colorful and playful), and a sprinkling of Christmas gifts, trees, wreaths, perhaps an elf, a reindeer, a Santa, snow, or whatever else says Christmas in an artist's eye.
Something completely different may be perfect, but I don't have the imagination to see it.
I would like the design to include the layers so that the text can be easily updated or changed, preferably in a photoshop psd, but InDesign will work, as well.