Phonetically Unpronounceable

XKCD is a popular web comic. It is both funny and intelligent.  The name was chosen by the author as they liked the fact that that collection of letters is phonetically unpronounceable.  Letters were made to represent words which are naturally pronounceable.  We wouldn't normally think about how we could arrange them otherwise.  So let's dive in and do the opposite of what we would normall do.

Your challenge is to create a set of 4 characters that is similarly unpronounceable. 

Try and make the most interesting quadruple of letters you can.

Leave them below as a comment and lets see who can come up with the best unpronounceable word.  We'll choose the winner by way of votes on the comment.

I sense creativity in you.  Use it to it's fullest.