Father Terrence Kardong, O.S.B., addresses this some in his book, “Conversations With Saint Benedict”
“To say that monks should cut back on ‘some chatter, some joking’ implies that they were known for doing some of both!”
“Benedict has a certain reputation as a sourpuss because at several places in the Rule he warns the monks against laughter. I would contend, however, that most of these texts need to be carefully qualified for various reasons. For example, in the Instruments of Good Works it is not just any laughter that is prohibited, but raucous, explosive guffawing.”
“As one of my now-deceased confreres used to say, ‘The best jokes in this place are walking around.’”
St. Benedict’s Rule set certain standards to maintain order, but in my experience monks do not leave their personalities at the door when they enter the monastery. Monks with a sense of humor will still be funny and joke, but at appropriate times and with caring, not mean-spirited, discretion.