Is there any point in giving someone a birthday card if the only nice thing that you can think of to say that doesn't make you gag is "Happy Birthday"? Because nothing else is true. Usually I would write something like "It's great to work with you!" or "You're such a fun person!"
or some such complimentary phrase. But what if you really dislike the person? What if this person recently stabbed you in the back in a completely egregious manner? Is it worth the gesture? Is the small political goodwill that it might engender worth your last card that actually says "Happy Birthday"?
Disclaimer: This post has nothing whatsoever to do with my working life. Which I strive to never mention here at all. In fact, I am not employed at all. Yeah, yeah, that's it, not employed at all.