A by-product of the use of the yourself when used to describe someone being hypocrytical. For example, "you are being a loser" someone typically would reply "yourself". Over time as "yourself" was continually sped up and said faster and faster it eventually ending up sounding like dolf which people have begun to say.
Recently people have begun to say "dolf your solf" for the only apparent reason of rhyming the words. This does however add offence implying that the person is continually hypocrytical.
"dolf" has also been used to end unwanted conversations very promptly with the quick use of the single cyllable word. A very effective way to get someone annoying out of your face.
"you are dolfed pal"
"dolf ur dolf"
"double dolf" (massively hypocrytical)