At first, used to describe off-kiltered things "this food is schmebbin'" or "those dance moves are schmebbin". . . it soon turned into meaning "to date, flirt or be interested in" such as "who are you schmebbin'".
Schmebbin' boils down to doing something you know you aren't supposed to be doing, but do anyways.
"I was schmebbin' on this girl, but decided to cool it off."