Indeed, I find it rather irritating to see "this" and "that" minimally reduced to "dis" and "dat".
However, to bring forth as an example "who dis" and diss (pun intended) only the "dis" part is rather inadequate. I would prefer the proper form of "who is this" as an improvement over "who dis".
However, I am aware that the colloquial "who dis" is perfectly acceptable in certain parts of USA or among certain segments of US population. I believe it is still not accepted as mainstream English as yet.
