Sorry you had a bad experience Rock Chick but it can work both ways.
Had a couple come to our session the other night, good musicians both of them. They started to play along with an unncompanied singer so I lent forward and asked quietly if they could just hang on a minute.
They took umbridge and didn't join in the rest of the evening.
It left me feeling bad for a while as we pride ourselves on being a friendly session.
There you go can't win them all!