When you start thinking of how much stuff costs by how many track tires that money would buy (racing units is the correct term).
When you start a thread in the detail subforum entitled: easiest way to get tire marks off paint.
When the UPS driver knows you by name and asks what your times were last weekend.
When you call the end of your driveway "turn 1"
When you people ask how fast your car goes you say: "I ran a 2:04 at Spring Mountain last weekend."
When you check tire temps and pressures in the parking garage at work.
When you buy a 40' pusher diesel motorhome so you can sleep in your own bed on track weekends and you can take the dogs with you. [yeah, I did that...and sold it]
When you can swap brake pads and tires (and bleed brakes) in less time than it takes your neighbor to check the oil in his SUV.
When a $3k set of shocks looks like a necessity.
'11 E90 M3, Mebourne/Black/Fox Red/Black, 6MT, roof, PP2, heated seats, moonroof, split folding rear seats, iPod/USB adapter, Technic harness, JL XD 6/600.
'02 E46M3, Imola/Black, 6MT, CWP, no sunroof, Ohlins, Eibachs, PFC DD rotors, PFC pads! HAT Clarus/Legatia speakers, 2 big amps in the back.
'05 X5 4.4i, Imola/Black, Premium, Cold, HAT Imagine 6.5's, Intravee iPod adapter