I know that this question is similar to asking whether "Dementors" in Harry Potter can laugh or smile, but still, in the canon do the Sith ever laugh, maybe at least smile? Do they understand jokes and do they have a sense of humor?
In Return of the Jedi, there are several instances where Palpatine is either laughing or smiling on the Death Star. He also does this in the Clone Wars, when he fights Darth Maul and Savage Opress.
As far as jokes, in Revenge of the Sith, Dooku responds to Anakin's "My powers have doubled since we last met" with "Twice the pride, double the fall". In Rogue One, Vader says "Be careful not to choke on your aspirations" as he is force choking Krennic.
There are likely more examples if you dig through all the material and look for them but these are the ones that stood out the most for me.