In How to contact professors for PhD vacancies?, Suresh suggests (and I believe most of you agree with this):
Think about their work. Find something intelligent to say (even a question).
I have read a couple of the recent, most cited papers of the professor. It is considered to be a breakthrough in the field, and of course very interesting. I have some questions, but I'm afraid that they are just trivial, that the answers are lying apparently in the papers (in the professor's perspective) that I can't see.
But I decide to write an email to them anyway. When I'm about to describe what I've read, I come up with a joke about that breakthrough method. That joke is only one sentence long, and for me obviously it's funny. However, I'm afraid there are some backfires if I decide to joke about it. Maybe the professor will see that the joke has no relevant to the method (explaining kills the joke), or it will be too informal in the first contact.
So is it safe to put the joke into the email?
TL;DR: Women rates funny guys as more intelligent. Are professors the same?