Instead of saying 'so' people may say 'sahhh'. It means 'very', 'really', 'extremely' 'very' etc. Used in Australia, mostly by teens, not to be taken in any serious fashion.
Today's history class was sahhh boring...
Essentially meaning 'I'm just saying', 'just casually' is most often placed at the end of a sentence, often preluded by an idea or statement that is commonly accepted as truth. As a result, it is most often used following an observation. 'Just casually' is a light phrase that connotates feelings of ease to others, as it often has the effect of putting less emphasis on the matter/issue at hand.
Kim Kardashian is totally hot, I would so do her if I could, just casually.