I recall an episode where Riker and Troy were getting back together, (Possibly the episode "Second Chances"?) and she disliked his beard, and so Riker shaved it off. Data noticed the change in the turbo lift, and Riker commented "Smooth as an android's behind".  After getting off, Data stops Riker, and asks "May I?" motioning to feel his face.  Data then made a disapproving expression and shook his head.

Whether one can call the above episode a "joke" is certainly up to interpretation, but it shows a certain humor awareness on Data's part that is not involuntary.

I remember this moment quite vividly, though I cannot place it in its full context. The subtleness of the moment seemed a little atypically human for Data.