[dahdum]

Right click a text file (such as "example.txt") and try to rename to ".gitignore". You get an error popup dialog "Rename: You must type a file name."

That's what he means...you can create it in various applications though.

[lucb1e]

That is the most annoying error ever. No, I must not! I shall decide for myself what I must and mustn't do! /me opens cmd.exe and uses ren untitled.txt .gitignore

A slightly bigger challenge is a file named CON :)

[nik41tkins]

Or .... , but that one is fairly easy as long as you COPY from the CONsole to a <fileName>. And remember ^Z to save and quit.