GGNOREKTHX is an abbreviation meaning
Good Game No Remake OKay
It is used as an enhancement to words such as 'pwned' or 'owned'. The phrase itself means that one has defeated another in a game, and declares that there will be no rematch, and concludes with 'okay, thanks for the win'
"dboss you noob ggnorekthx"
"zediabolical u sux ggnorekthx"