The symptoms:

Denial - The person in question will often concoct half-baked excuses such as: "I'm not a peak bagger, I'm merely an avid outdoor person who likes to climb mountains. I can stop at any time." (Don't be fooled).

The 'List' - All peak-baggers keep a notebook of some sort, which contains 'The List'. The List records successful ascents, and associated informatiion like the date and elevation of each climb (kind of like this site, eh?). Typically, the peak bagger will keep the notebook underneath the mattress or at the bottom of a sock drawer. Consistent with the denial symptom, they rarely refer to it as a "Peak Bagging List". They usually call it a "climbing log".

The 'Look' - Peak baggers will usually have a far off look in their eyes, as though they are scanning the horizon for new climbing goals. They may seem aloof a great deal of the time.

The 'Walk' - Peak baggers can sometimes be identified by the deliberate way they walk. They have that determined, measured 'rest-step' cadence even when they are just headed to the fridge. They also tend to wince in pain with every step during the summer months as a result of excessive wear and tear on their feet and/or knees.

While attempting to determine whether or not someone is a peak bagger, there are some other signs that you can look for. For instance, the peak bagger:
  1. may mysteriously disappear from the city every weekend.
  2. has really high mileage on the ol' 4WD
  3. buys hiking boots in May and needs new ones in July
  4. rugged appearance (leathery skim, mussed hair, definite "Old Spice" commercial material)