when a band plays and a guitarist makes an obvious mistake, the WORST thing they can do is make an angry face!!! you must shrug it off or even better laugh about it :D your conduct on stage has a direct effect on the the crowds feeling toward you..if you make a mistake and look pissed the crowd will take that to mean you would rather not be here playing for them....they rarely think your mad because you muffed that note...the crowd feels/feeds off your energy so you must convey you are having fun and in turn they will enjoy the show.
here is an example of a dumbass http://stupidity.com/play-8264-Axl_Rose_Walks_Off_Stage.html