...you use <TAB> characters to align text.
...you use <TAB> characters for any purpose other than introducing a command line in a makefile.
...you drink bottled water even when there's coffee, sodapop, or a drinking fountain nearby.
...you have never entered xyzzy on a commandline.
...you can't copy a file via the commandline.
...you can't find the commandline.
...you don't know what a commandline is.
...your filenames contain embedded blanks.
...your filenames summarize the content of those files so completely that the content is pretty much redundant.
...your email is 2% content and 98% HTML code.
...your reply comes before the quoted text.
...that quoted text is the entire message to which you're replying.
...the signature of your email is longer than the body.
...you think re-installation is a reasonable way to fix a misbehaving program.
...you can't understand why vi fanatics and EMACS fanatics don't just use Word.
...you don't know that Linux is mostly GNU.
...you don't know that Linux's response to make love isn't nearly as amusing as that provided by older unices. (Don't know how to make love, or, sometimes, even better... Not war?.)
...you don't know that even hpux man pages once had a sense of humor.
...you believe that the only fix for slow software is faster hardware.
...you think that the English word data takes the plural form of verbs.
...you pronounce SQL like sequel. (It's squeal.)
...you pronounce URL like Earl. (It's U R L.)
...you call directories folders. (They're directories.)
...you call / a backslash.