Leave me some feedback if you want a pattern. The buttonhole was just a hole stretched inbetween the stitches. I used cotton worsted weight. The buttonhole end was actually straight, and looks peaked because it stretches as it fits the cup.
Good luck. I cast on 14(I think) and garter stitched 4 St for each side. Pretty sure I cabled 3 and 3. I knit until it fit the mug.
Great for a stack of Xmas gifts. It takes a couple of hours to make and it fits a straight sided mug.
Send me a comment if you want a few good free links to similar patterns.