I spy an inexperienced musician

A friend of mine reckons you can tell an inexperienced guitarist because only an inexperienced musician will do a gig and rest their drink on an amplifier. His point being that sooner or later, someone on the stage will knock the drink over and possibly ruin some expensive equipment. I had to agree with his point as it was hard not too but I have a slightly different way of spotting an inexperienced musician. To me an inexperienced musician plays crap music! I think the best way to learn a musical instrument is to fall off the horse, get back on and fall off again but please don't do it when I'm in the audience.