Seeing the other posts about pens, here's one I thought of immediately . . .
In a couple of situations, I will only use red pens or markers to write, and specific red pens or markers, at that.
At work, I will only take/make notes, etc., with a RED Pilot Precise V5 Extra Fine Point Pen. This quirk of mine is so well known at work that if I'm at someone else's desk and have to make a note about something, usually they'll ask me: "You got your red pen on you?" 99.9% of the time, I do. If I don't, not an eyebrow is raised if I say: "Nope, hang on a sec." I come trotting back with it and scribble whatever.
My preference for writing with a red pen is so well known in the office that if somebody brings a work order to me to make a note on, sometimes they might bring a red pen with them for me to write with. That's really sweet and thoughtful, but I never use the one they bring because it's not a Pilot!
In addition, I usually keep a backup Pilot in the car and at least two in my desk drawer as backup. No one is ever allowed to use my pen unless I'm standing right there and they give it back to me immediately.
The ONLY time I have EVER deviated from this is if I have to sign off on some sort of official paperwork that must go out of the office. And then I will ONLY use black ink. Don't come anywhere near me with a blue pen for that.
At home, except for three of them, all of my VCR tape labels are written with RED Fine Point Sharpie markers, only. I will not make a new label if I don't have a red Fine Point Sharpie marker.
Scribbling notes at home for myself, writing anything else . . . I don't care what color ink or pen I'm using. I've been known to leave my husband notes in DayGlo Purple, or Hooker Orange, which sets his teeth on edge!
He'll mention it, and my response is to shrug and say: "Hey, it was there, it worked . . . what's the big deal?''
THIS coming from me, who will only use red Pilots at work and red Sharpies at home for the VCR tape labels!