In this instance it was not a Jam session, but a session where people played and or sang as individuals, even had it been a Jam session if one person leads with a 12 barre it is not appropriate for someone else to start laying down a reggae rythym, all that happens then is a discordant noise. What Raggytash encountered was someone playing at odds with the rythym he was using, not the best guitarist (as he himself will admit to) in the world he was put off by this and the person in question was asked to stop but carried on regardless. Raggytash is seeking a way to ensure he can get someone to stop without offending them