Coming from the original word 'retard', or 'retarded', wetawd or wetawded may take it's place in any sentence. It is used to 'poke fun' at it's mother word 'retard'. By doing so it is not as offensive or harsh. It also implies a sense of irony, in that you are too retarded to actually pronounce the word correctly.
You may also use the word wetawd when watching someone do something really, really stupid.