The abbreviation could be interpreted as standing for “goddamn church.”
I just see it as something like “g-d church”. I don’t get it either. 
When my grandmother wants to cuss (like maybe once per decade), she’ll say “gee dee” instead of “god damn.” It’s not uncommon in certain populations of Americans, probably mostly elderly feisty yet Catholic ladies. As in “Ooooh, that cashier didn’t give me double coupons, and it’s DOUBLE COUPON DAY! Well … (long pause) … gee dee!”
I do hear it enough that when I see “G D” written, I usually think “god damn” right away.
It seems the SDMB buffer is Hippopotomonstrosesquippedaliophobiac or Sesquipedalophobiac - Fearful of long words. 
The real word for the phobia to the number 666, Hexakosioihexekontahexaphobia, appeared when I did a search for it.
My dog, Duchess, has the tag number 666 this year. I imagine that this particular tag has been passed up by several persons before we got it. I was very amused that Duchie is this year’s Devil Dog.
(Being a small terrier, she hardly fits the image of a slavering Hound From Hell, but she does remind us a lot of Dog from “Good Omens.”)
How about Joshua? Since that’s the English version of Jesus, and we all know that Satan loves to co-opt things of God’s. 
Thanks, delphica.
Oops, I forgot, many thanks delphica from me too for that gd explanation.
When I worked at Cirlcle K, I rang up a customer’s sale to $6.66. He immediately grabbed a piece of bubble gum and slapped it on the counter so I could retotal his sale.
When I lived in Oklahoma several years ago, a proposition came up for state wide vote. By law, propositions are numbered sequentially, and this one was, you guessed it, Proposition 666. Proposition supporters tried to get the number changed, but apparently there was nothing in state law for such an eventuality. I don’t remember what the proposition was for (just that it was something benign), but I do rememeber that it lost in a land slide, as expected.
It would have been perfect if the name of your dog was Nero:
When I worked in a law office, we had a numerical filing system, and yep, a new client got 666 as their number. It truly blew my mind when they asked to have a different number. Gotta love our office manager, who just sent out their billing statement without the number, but left it as-is for internal office handling.
It amuses me no end that the Hebrew words for “Jesus’ name” enumerate to 666. So when Christians pray “in Jesus’ name, Amen”, they are invoking the Number of the Beast.
The telephone prefixes in my town are 662, 663, 664, 665, and 667.
I live in Topeka, Kansas, home of Fred Phelps. One of his schticks used to be that the whole city is irredeemably evil, because our 5-fogot zip codes all begin with 666 :rolleyes:
Fred Phelps knows the addresses of the 5 fogots in Topeka???
I hope they have good locks on their doors…
All this numerical superstition reminds me of an interesting incident from days gone by. Back on July 7, 1977 (7/7/77), a bunch of folks at Ak-Sar-Ben (the horse track in Omaha) decided it would be a great idea to bet on the 7th horse in the 7th race. After all, 7 is a lucky number. How could they lose? A staggering number of bets were placed on this horse. And the outcome?
Wait for it…
It came in 7th. I kid you not.
Truly poetic justice.
Are you sure it’s true?
I’ve heard it told as a joke (with various numbers) dozens of times…
Took a moment, however my Google fu came through: I did remember a similar story, but from a different location:
I worked with a woman who forced the phone company to change her mother’s phone number because it ended in 666. I can’t remember why this came up in conversation, but when it did I called her stupid to her face.
Regarding U.S. 666, I thought they changed the number because people kept stealing the highway signs. 
What’s really sad is all the future generations who will watch Natural Born Killers and not know that it was a real highway once…