Don't Piss Off da Sound Person!
Years ago I was in a band that was sharing a bill in San Francisco with another band that will go unnamed. When we arrived the other band was doing their sound check. The band leader was getting bent out of shape by something about the sound and was communicating his frustration in a rather terse manner, putting his band mates on edge and clearly irritating the sound man.
My band mates and I were astonished at this guys behavior and we hoped that we didn't all get tarnished because of it. After what seemed like a long time this guy walks up to the mixing board and tells the soundman that he is free to go and the bandleader will do the sound. Just a split second after the soundman dropped the f bomb on him, the bandleader smacked him across the face.
Well, that was the end of that. The show was cancelled and said bandleader had a hard time booking shows in San Fran after that.
Moral: Be nice to the sound person! Here's a little article you can read...