Rules for playing with others. Please feel free to add your own, I'm interested.
1. When someone brings a new song, do not play along. Listen, discuss, then play along.
2. When there's a break, and someone is talking, don't noodle with your instrument. Listen
3. When the session is almost started, and someone else has their instrument out before you, and starts playing a riff or a progression, or even a song, DO NOT get out your guitar and play something else. Try to blend with the original fellow.
4. Your turn.
I have had all these things happen on more than one ocassion, and I'm getting to the point that I hate playing with others. Really hate it. Everyone seems to do these things mentioned above, and I can't for the life of me figure out why.