A bummer lamb is an orphanedbaby sheep that has to be fed with formula from a bottle. When you call someone by their name and add bummer, it means they don't like crowds and prefer to stay much to themselves.
Guy 1: Dude, I heard you were seen in an alley with State-Street Stacy last night.
Guy 2: Yeah dude, she gave me a bummer in exchange for a KFC famous bowl.
I was walking through the alley and convinced the toothless lady begging for change outside the bar to give me a bummer. Only cost me $5, best $5 I ever spent