I've had this honour a couple of times. What i did was go straight into a relevant but funny joke/story and get them all on your side by laughing. That made me comfortable and them. Also, they forgive you if you happen to **** it up a little. In my case I started with "being asked to be best man is rather like being asked to make love to the queen mother.........it's a great honour to be asked, but i'm not sure I'm going to enjoy it.". The audience were mostly devout catholics, they loved it. That was a few years just ago before she passed on.