Question 16: Some people speak words that are tantamount to Kufr (disbelief) or Fisq (flagrant violation of Islaamic law) and justify it by saying: I am just joking. Are such people pardoned for doing so if they are only joking?
Answer: It is strictly prohibited to tell blasphemous or bawdy jokes. Allaah (Exalted be He) says: If you ask them (about this), they declare: “We were only talking idly and joking.” Say: “Was it at Allaah (عز وجل), and His Aayaat (proofs, evidence, verses, lessons, signs, revelations) and His Messenger (صلى الله عليه وسلم) that you were mocking?” Make no excuse; you disbelieved after you had believed. Those who behave as such should make Tawbah (repentance to Allaah) of it and ask Allaah for forgiveness in the hope that Allaah may pardon them... read more here.