if you are in a instrument jam or a song circle, and if it is very unusually good, let the music be the top priority. Don't break a good flow of songs or tunes with something silly or out of the flow of music and, again, if it is an exceptional collection of people or whatever, let them take over if you are not up to speed or at their level and you will hear exceptional music. If you are more interested in taking your turn or singing something out of the blue book, the music will suffer and you will have lost a very rare opportunity. This would be the exception rather than the rule of course.