Most of the times the therapists are not humorous in order to not offend the clients in anyway. But every therapist has their own approach with the clients, some more structured than the others.
You can communicate to your therapist that you wish to have a more humorous interaction. And a therapist will understand your intention and not judge you for asking that. But being humorous also depends on the therapist and if he/she is comfortable with that format. Therapy is a collaborative approach of both client and the therapist and it is important to clarify the approach you prefer with your respective therapist to see what works with both of you.
Hope I clarified your doubt in this regard.
Nandana Priya Kamasani