While taking a shit in a cup, having a girl simultaneously shitting on your back which rolls down into the cup and after cumming inside the cup, make the girl drink it.
Millishit, in the metric system denoting a factor of one thousandth of a shit. If you give a shit, it means you care about something. If you don't give a shit, it means you don't care. So a millishit means you REALLY don't care.
The product of having extreme hardcore anal sex with someone who has to take a shit. The feces are left mushy and loose often seeping from the anus in a soft milkshake-like form.
Miranda: Are you ok? You're walking a little funny.