When you go to lunch and purposely or accidentally don't invite someone.
Alternative definition: You're the last person to get your food at the table, well after everyone has gotten their food. restaurant
Or Dinner Finger
Don't invite Mike, we gave him the lunch finger. Or oh, no we gave Mike the lunch finger...oops. Or sorry, we didn't mean to give you the lunch finger.
Or Andrei always gets the lunch finger here, I think the Waitress hates him....