stands for end of universe, you can also say 'eoe' for end of everything, or eoi for end of infinity, they are all used when you want your insult to be the final insult, so you end the universe/everything/infinity knowing that you won the arguament even though you had to end the universe to do it.
frank: damn i pzzwn
reuben: oooooh man your teh fatness
tom: wtb (what the beast) you guys suck, i prwan
frank: you guys are both teh newbz full stop, eou