Autistic. There are many levels of tist. An alternative to the words and phrases, "retarded", "Mentally challenged", or anything else you can think of to describe someone who exhibits the kind of behavior that is frowned upon to point out in public.
Yissed is more than being just pissed. More like a “push me out of a window already” kind of pissed. You’re SO pissed off you couldn’t be bothered to write or pronounce the word pissed correctly.