Programmers, you know, are already incomprehensible strange creatures to outsiders, so naturally there's no need to show off to them.
So, how to show off to other programmers is a subject with real depth.
1. Programming Languages
Never ever ever ever say you're a Java/C#/C++ programmer.
Try to learn some weird languages. Python is already becoming too common; it's fine for writing, but you can't use it for showing off.
Lisp and Erlang are both excellent languages for showing off.
Of course, if you claim to know Haskell, that's even more badass. If you really don't know it, no problem—posting status updates about Haskell also makes you look impressive.
When you have nothing better to do, you can also trash-talk Java/C++ on forums about their shortcomings.
But what if the other person strikes first and mentions a weird language name?
You can say with a smile, "Do you know that all languages in the world derive from Lisp and Smalltalk?" Guaranteed to leave them stunned for 3 seconds.
2. Operating Systems
First of all, definitely don't use Windows. Only Muggles use Windows.
As for Linux, Ubuntu is a bit lacking. Nowadays quite a few people are already using Arch.
Those in the know all realize that Gentoo and LFS are the real show-off weapons.
Compiling everything yourself and all that—this pose isn't something just anyone can pull off.
Going even deeper, if you work on a Lisp Machine, you're almost god-like.
3. Editors
As a member of the "IDE Shall Die" group, I admit that to a large extent I'm just showing off.
A plain text editor is your ultimate destination.
Vim is the standard, but only Emacs deserves to be called a divine weapon.
"The editor disguised as an operating system" is no empty boast.
Of course, if you want to show off well, you also need to learn its configuration language, Emacs Lisp.
4. Blogs
Writing tech blogs on CSDN/ITeye/EOE/cnblogs is indeed much better than writing tech blogs on Renren.
But you should know that the big shots all have their own personal websites.
Moreover, one common point is that their websites are written in raw HTML (no CSS) and look extremely ugly.
The whole site radiates an aura of "My articles here are so great that the interface doesn't matter at all."
For example: http://xahlee.org/index.html
5. Others
I'm used to calling people who can't write code "Muggles"; you can have your own terms too.
Don't write Linux/Unix; the correct and professional way is *nix.
Don't keep technical books at hand. Even if you want to put out a book or two, make them self-printed, all-English manuals.
Or writing code on paper with a pencil is also a good option.
You can also develop some peculiar habit, such as claiming to be a Lisper and then adding (parentheses) everywhere.
6. Advanced Show-off Techniques
Showing off all the time won't do. So I've been looking for a show-off method that instantly destroys all programmers.
To be honest, there are three kinds of people in the programmer's world.
Most are Muggles who can't write code, then there is the group of programmers itself.
They believe the only people more badass than programmers are those who do mathematics.
So, if you really want to show off your badassery, go and master the Fourier transform.
(Also: the inventors of Lisp and Python were both mathematicians, and the great Donald Knuth is also a math professor.)