Shit n' Ditch is the act of using the restroom at a restaurant, convenience store, drug store etc, and leaving right after you 'do your duty'. It's just meant as a pit stop to relieve yourself, and it often causes awkward stares with the employees working there, who know you're not going to buy anything. Sometimes you can't use a restroom because the facility might have it reserved for customers only. This would be considered an unsuccessful Shit n' Ditch, and you would have to find another place, quickly.
where were you?"
"Sorry, I did a Shit n' Ditch in the Chipotle
across the street."
2. "Hey is there a restaurant around here? I need to do a quick Shit n' Ditch."