I'm not really a musician, but as an actor I think that any live performers always deserve respect. So always make a point of applauding after at least 2 numbers even if the rest of the pub isn't paying any attention to what's going on.
If the band is actually good, and I've had a few, I have a tendancy to lurch up to lead singer and say ' You were great you were, can I buy you a drink, I'm an actor you know, wanna come and see my play?' .. and then wait until a kind friend gently leads me away.
Since playng bass I will definitely watch bass players in future for good tips! But will try not to get drunk and harass them inappropriately afterwards