Ironically enough, dirt sandwich can mean just about any positive word you can think of. Some synonyms would include awesome, cool, amazing, legit, bodacious, etc. Also, if you're in a rush and want to define something as any of these words, "dirt" is an appropriate abbreviation to dirt sandwich. This word is best used in a louder than normal voice, and when typing it is most appropriate to type it in all CAPS.
I could a 100 on my last Biochemistry test...DIRT SANDWICH.
That mega fine honey over there is pretty dirt.
Guess what my mom packed in my lunch today? A dirt sandwich (this could mean any number of items...such as Gushers, Fruit Roll-Ups, a Snack Pack, or candy)