Me and a couple of friends were able to implement the game of Nibbles (Snake on old Nokia phones) in 70 bytes. Someone else managed to accomplish it in 48.
Someone would always eventually post "echo Hello World!" and the endless arguments would ensue about whether or not that was actually a program.
$ cat /tmp/hello
hello\ world
$ /tmp/hello
/tmp/hello: line 1: hello world: command not found
$ cat >hello
Hello\ World\!
$ chmod +x hello
$ ./hello
./hello: line 1: Hello World!: command not found
* fix: adheres to Hello World! standard now