You know you’re a monk when you say, “Hey, Abbot,” and you’re not Costello.
You know you’re a dispatcher when you use “10-4” or “copy” to indicate an affirmative response to a question posed to you by someone sitting in the passenger seat of your car.
Or if you read this and think, “Huh? What’s the joke? That’s a perfectly reasonable approximation.” (guilty)
I knew you were a cool person, Podkayne!
Other RadCon approximations:
2 + 2 = 5
1 over two to the fifth power is approximately zero. (Used to estimate when an isotope will be all gone - “After five half-lives it’s gone.”)
And, of course, the classic: pi squared equals ten.
And pi~1.
I prefer pi ~ e ~ 3.
You do not even bother to explain to people who have not yet seen the elephant themselves. You used to try, but now you realize that it cannot be done.
You know you’re an engineer/mathematician when you describe driving from Baltimore to Memphis “along the hypotenuse” (through West Virginia and Kentucky) as opposed to “along the adjacent sides” (though Virginia and Tennessee).
(FWIW, when I have to approximate pi, I use 22/7).
I’m also an amateur musician, and I knew I was a Dobro player when someone handed me a standard guitar to try out, and I flipped it into my lap.
You know you’ve settled into the software profession when you start talking about risk outside of work.
You know you’re a AutoCAD drafter when you hit the Escape key repeatedly to make your computer stop doing something, even though you’re not using AutoCAD.
You know you’ve been using AutoCAD for a while if you can still remember having to exit Windows 3.1 and boot up in DOS in order to run AutoCAD.
You know you’re a teacher when you have to resist the urge to correct other people’s children in public.
You know you’re a tech writer when you have to resist the urge to mark up the manual for the latest gadget. Or the bookshelves you just bought… :smack:
you know you’re a porn star when your employer calls and you say “not today, i have an ass-ache.”
You know you are a thoroughbred horse owner when your friends look shocked when you tell them the exciting news, “My four-year-old FINALLY broke her maiden. Better late than never. I am just glad I was able to be there to watch!”
Or when you tell your buddies at the track, after the horse you bet won, “I am so glad I didn’t get off Shagging! I almost got off Shagging when I saw Your Sweet Lips. But I love Shagging on the grass, so I figured Shagging would beat Your Sweet Lips in the mud.”
You know you’re a banker when you’re interrupted while reading (or sleeping, or talking on the phone, or any number of things) and mutter “Wait just a minute. Let me complete this transaction.”
you know you work retail when you find yourself saying “Have a great day!” to everyone you part company with.
You know you’re an editor when you find that the fictional paperback novel you just bought for your own personal enjoyment has so many errors that you can’t help but mark them all in red pen - and you find it difficult to stifle the urge to hunt down and interrogate the editor who missed them. 
You know you’re a topologist when you stop off in the morning at Krispy Kreme and order a half-dozen coffee cups.
You know you’re a computer programmer when a woman in a bar comes up to you and says “Hi”, your reaction is…
if (woman.hotness() >= (self.hotness() - 2))
cout << "Can I buy you a drink?";
else
throw new RandomExcuseException();
You know you’re a project manager when, whilst planning your mates bachelor party, you seriously consider sending the invitees change request forms because you just know that at least one of them are going to changes plans at the last minute or do something else that requires it.
Even worse if you discuss it with the groom (also a project manager) and you both laugh about it
No, I didn’t actually do it…but I DID think about it
grey_ideas
Equally guilty.
You know you’re an astronomer when you make up ludicrous names for telescopes and classes of objects just to get a cool sounding acronym.
From a list that’s been circulating around in emails for years…
You know you’re a geologist if:
[ul][li] You have ever had to respond yes to the question, “What have you got in here, rocks?”[/li][li] You consider a “recent event” to be anything that has happened in the last hundred thousand years.[/li] You have ever uttered the phrase “have you tried licking it?” with no sexual connotations involved.[/ul]