xinsult -- the X11 server of choice when you want it to mess with your mind.
Part of my ongoing plan to write an SDL-based X11 server, this program, which uses SDL and SDL_net, functions as a partial stub for one. X11 clients can connect to it at localhost:99.0 but instead of actually doing anything, xinsult just returns a cryptic, insulting, and/or disturbing error message before breaking the connection. (Windows® Screenshot) (Linux® Screenshot)
I'm sure you can see the utility.
Code is freeware and comes with no warranty stated or implied, has not been thoroughly tested, may set your dog on fire, does not require a dog, no purchase necessary, connections of non-native endian not currently supported, streams other than TCP/IP not supported, opinions expressed by xinsult bear no relation to those of the author, yada yada tiny print.