This would be an acceptable reason to laugh at a funeral...
A very prestigious cardiologist died, and was given a very elaborate funeral by the hospital where he had worked for most of his life. A huge heart, covered in flowers stood behind the casket during the service as all the doctors from the hospital sat in awe. Following the eulogy, the heart opened, and the casket rolled inside. The heart then closed, sealing the doctor in the beautiful heart forever.
At that point, one of the mourners just burst into laughter. When all eyes stared at him, he said, "I'm so sorry... I was just thinking of my own funeral… I'm a gynecologist."
The Priest fainted