If you mount a back up optic on your weapon because your first choice may fail on the range while being attacked by the paper bandits.
If you must absolutely have it black!
If you wear your combat boots bloused while visiting the mall, with your BDU pants and 'I love my Glock' t-shirt. (actually witnessed this rare event)
Carry a pistol in a shoulder holster, with a back up pistol on your hip, and another on your ankle, a can of MACE on your belt, a tactical knife beside it and a stun gun. Just in case you need a little more than another magazine.
You think carrying another pistol is better than, two more magazines.
Actually on that note, thinking you need more than one back up magazine for a CCW.
Say a bolt action is a piece of junk because it takes you too long to empty the magazine.
Being an ass to someone because they don't like what you do. Examples, Not liking the AR, the 1911, or Mossberg 500 shotgun.
And my personal favorite, Having to decide between your green laser/flashlight, and a back-up sight, red laser/flashlight, normal flashlight, ammo carrier, snowcone maker, asphalt speader, coffee bean grinder, or espresso machine.