I've had several friends who say a short form of "casual" but how to write this? CASH - obviously not CAJSH - huh? CAJZ - uh, no Any ideas?
If your question is how you phonetically spell out the sound like the s in casual, people generally go with "zh". "Cazh" still looks strange, though, so I'm not sure how much this is going to help you. If this is for dialogue in your story, maybe try giving the character(s) some other kind of unique way to say something else that will be easy for the reader to handle instead.
Um... in dialogue, if people are talking about something being casual dress, I hear it referred to a lot as simply "cas dress." Phonetically it sounds like 'caz' That's my input. ~Lynn
If it's slang that is being used often, I don't think you need to treat it differently than any other non-phonetic word. Just make it clear what "cas" means the first time you use it, and you're good to go.