Investors who bought Starbucks stock this year are likely eager to kiss 2007 goodbye, as shares of the world’s largest coffee shop chain have tumbled over 40 percent since January on concerns about slowing U.S. customer traffic, rising dairy costs and competition from fast-food rivals, such as McDonald’s.

But 2008 could bring the Seattle company a new headache, according to one analyst — a knock on the door from shareholder activists.

In a research note on Starbucks on Thursday, Friedman Billings Ramsey analyst Howard Penney warned that “the dramatic downturn in the company’s fundamental performance is likely to create issues that it has never faced before as a public company — shareholder activism.”

Penney cited recent investments by activist shareholders in restaurant chains Panera Bread and The Cheesecake Factory for his view.

“It is only a matter of time before one appears and starts to put some pressure on Starbucks,” he wrote.

Finally, Penney channeled the Christmas spirit to list his “key points” on Starbucks:

On the twelfth day of Christmas, Starbucks gave to me…
12 - Signs of traffic humming
11 - Improved new unit volumes
10 - Speedier baristas
9 - More transparency
8 - Product inn-o-vation
7 - More global growing
6 - Rising ROIC
5 - Slowed U-S growth!
4 - Four-wall initiatives
3 - Three new desserts
2 - Two new board members
1 - And a change in U-S strat-e-gy!