Hot piss is a exclamation much like wow or cool! It can be used in a variety of ways and is quite flexible.It can be adapted for both happy and sad situations.
A lesbian ritual in which a lesbian dominatrix urinates into an enema bag and then immediately inserts the enema tube into her lesbian slave's anus and releases the full contents of the enema bag into her slave's intestines.
Or, sometimes a funnel is inserted into the slave girl's anus and the lesbian dominatrix urinates directly into her slave's rectum.
In either case, the maximum temperature of the lesbian dominartrix's urine is retained, thereby the name "hot piss enema".
The act of taking an angry shit in the middle of Nevada desert while on a 9 hour road trip after you have eaten nothing but Mexican food and drank cheap beer.