1) You put on your jeans and they already have the right leg rolled up.
2) You do laundry when you don't have any more clean bike shorts.
Your rain jacket loses it's water repellent properties on the morning it's pouring outside.
You were planning to re-seal it this weekend, but the brand new bottle of Nikwax you just bought fell off the top of the washer/dryer stack and broke. Your jacket is no longer waterproof, but you wear it anyway.
You're riding to work in the rain and look at all the people staring through the bus' foggy windows and you're feeling sorry for them!
Not sure if this was already said yet...
You wear spandex outside the health club.
Ball Powder; Gold Bond is good.
-you need to 'powder your donuts'
You machine your first rim, you machine your first hub.
You raise your own cow from a calf and harvest the leather to create your first suspended saddle...
you assemble a bicycle from a pile of parts, you build your first wheel, you know you are addicted to bicycling when you build your first frame.