I've never seen anyone downvoted for an otherwise substantive comment that included humor. However, if a short, pithy comment offers nothing besides humor: 1.

I've never seen anyone downvoted for an otherwise substantive comment that included humor. However, if a short, pithy comment offers nothing besides humor: 1. It doesn't gratify one's intellectual curiousity. 2. It's probably not original and probably not even very funny.