Everyone else is lying. As allude to in >>12, it really mean "shat on (while) with the loli", meaning that the poster was with a loli, and then got shat on. The shitter is most commonly depicted as Mona, but also sometimes Squeeks or Grandpa, and the shitties are usually Grandpa and Shii, but also sometimes Junior and Mittens or Giko and Shii.
God I hope you die.