Lolski is an interjection used originally by internet trolls, but it's use has become common throughout social websites and messengers. It is usually exclaimed after a bout of hilarity, most commonly occurring in video games and message boards.
David throws a banana peel in front of Adam, who trips and face-plants; David's responds with a definitive "Lolski!"
Lolki Lawlingontheflorollin is the mythical being of mischief in Troll mythology, a son of the giants Fatty and Lawley, and foster-brother of Trolldin. He is described as the "contriver of all fraud". He mixed freely with the gods for a long time, even becoming Trolldin's blood brother.
(Taken from Encyclopedia Dramatica)