In the Valencian language, xe is used as a conative interjection for calling attention to a subject, or as an expressive interjection. Used as an interjection, xe may be positive or negative in nature to express, grief, anger, frustration, surprise, joy or praise.
The Catalan/Valencian language group is spoken in the eastern Spainish regions of Catalonia, Valencia, and the Balearic Islands, as well as on the Italian island of Sardinia, and in the French département of Roussillon. Xe is the equivalent Valencian spelling of the Catalan che.
Phonetically, xe is pronounced tʃe in the Valencian/Catalan dialect. To an English speaker, this would sound like, "chay".
A quick study of linguistic references agree that the Catalan/Valencian dialect has hundreds of such interjections, most of which have no formal direct translation to English. I am no linguist but it seems that, informally, I might conclude that xe might be equivalent to Dude in American surfer/stoner culture? Google offers a Catalan to English translator that I have used to make the following examples:
"¡Che, aconseguir els seus peus del sofà!" – Dude, get your feet off the sofa!
"¡Deixa per aconseguir una mica d'herba bona, che!" – Let’s get some good weed, dude!
"¡Cheeeeee...!" - Duuuuude!
The same usage of the interjectory che can be found in Argentina. Catalan speaking peoples were among the Spanish immigrant population in Argentina. No doubt these migrants lent che and many of their other colorful interjections to Argentinean linguistic culture.
Post-Script Ernesto Guevara, infamous Argentinean-born cuban insurectionist is more widely known by his nickname, "Che" as DonJamie points out.
I still wonder what Ancientsnow would say?
References:
http://books.google.com/books?id=nebMvGfMGeMC&pg=PA184&lpg=PA184&dq=Xe+interjection&source=bl&ots=jS_dpNDQPH&sig=rtscp5NusXWLHv5dWHMoJeALiMY&hl=en#v=onepage&q=Xe%20interjection&f=false
http://en.wikipedia.org/wiki/Catalan_language
http://en.wikipedia.org/wiki/Wikipedia:IPA_for_Catalan
http://translate.google.com/?tl=ca&q=undefined#en