I would suggest making a referrence to something the deceased found funny and something that most people there will quickly recognize as his sense of humour.If you go with a regular ice-breaker joke it could be seen as very tacky, or even inappropriate.
Hear is what you should say instead of a funny joke or story:Listen people this person lying right here is going to be fine. He/She will be in heaven where God and Jesus will take care of him/her. So brighten up, have a little spirit, and be happy this person is in a place where nobody can hurt him/her.
It's ok to make jokes at a funeral as long as they are tasteful. Make a joke about the deceased person. Tell a funny story about them. Encourage others to tell something funny about them. Keep it light, but tasteful. I wouldn't go just telling any old joke, that's just not appropriate at all. How well you knew the person makes a big difference in how much joking you should do at their funeral service.