An expression that implies one is being overly subtle while doing something common - such as talking. Similar to the way one would urinate on the bowl of a toilet or urinal to avoid creating an audible noise.
A saying that implies not to ruin everyone else's day (used in the context in a large group of people)
*At a party*
Person one: Looks like everyone here really likes this music!
Person two: I'm going to turn of the power, this music is trash.
Person one: Man, don't piss on the dance floor.
In football, to urinate on the playing field. You need to be a very important person to get away with this. So, if somebody can piss on the field, it means somebody who is well respected and generally pretty cool.