You know you're an audiophile if--

you tweak your friend's system
while he is out of town...

You sit for hours in infinite bliss listening to music just to hear what might happen next while all your ADD friends are out twittering.

you spend an excessive amount of time, listening to music, buying and selling components, and talking about the hobby.

what constitutes "excessive" is determined by a panel of psychiatrists or psychologists.

the hobby can be a disease if one neglects other important activities of living.

If you own a set of stax cans and they are more expensive than your car. :)

If your friend or family member ( mostly much juniors in age ) casually ask you to help them with a tip to improve their 2ch audio system set up ( with a very modest budget in mind ) and you keep explaining to him/her all about the sound quality and the equipments matching , till the person who asked gets emmensely bored and almost regrets asking you.