Another thing you may want to include in the best man speech opening is your introduction.  Introduce yourself to the audience and tell the audience a few words about your relationship with the groom - and maybe even the bride (preferably do this after a very funny opening joke).  It is a vital part of the best man speech, but if you stick it between two really funny comments or jokes, you will be golden.  For example, have your funny best man speech opening, introduce yourself, explain your relationship with the groom, and then include a funny story or funny fact about the groom.