You could use a program like Hex Workshop or ResHacker
If you use reshacker, then you can change those strings to whatever you like (as long as you find the strings)
if you use "hex workshop" then you must overwrite the text with a random letter or so... like x0x0x0x00x0x0x00x0x0x0x0x or whatever you like...
But these two programs are the best.. and then pack it with UPX
(to reduce size, and to crypt the code some more)
if you hex edit the upx-crypted exe and replace the text UPX (apperars 3 times early in the file) with any other three letters, then you cannot decrypt it using UPX later...
so then your buddies would have to run it,inorder to see it...
But make no viruses please... and make it possible to REMOVE your joke from the machine...