In the guitar store; always make sure you play the loudest in the store. After all, you never know when you'll be discovered. Besides, playing loud and fast means you're really really good. Be sure to scan the crowd to see who's impressed while playing.
Don't play something the other customers don't know. Stick with the classics like Stairway To Heaven, Blackbird and maybe some Floyd. Better yet, just learn the main riff to Smoke On The Water and play it over and over. If you already know some fast heavy metal sounding finger exercise, just play that instead, it makes you sound like someone who knows their way around the fretboard.
And always have some slaggy looking chick with you that looks bored. That tells everyone you play a lot as she's heard it all before, and that you're good enough to get the girl.
Be sure to wear something that leaves its mark on the guitar like studs and sharp pointy wristbands. This might be the only mark you leave in music, so make it a lasting one. Also, only old wimps strum a guitar... use that powerful sawing motion instead that you saw some guy do on TV. Be sure the pick scratches the upper portion of the guitar or you're not doing it right. When you're done destroying the guitar you can't afford, move on to the next one.
Anthing I've forgotten?