We did yuppies once. Matching pink polo shirts (we made little alligator logos and taped them on), called each other "Tad" and "Buffy", carried tennis gear.
This year's plan for halloween is Al and Peggy Bundy from Married with Children.
This isn't really a couple but a girl in my chapter and her boyfriend were Beavis and Butthead. It was extremely funny. They made their own shirts and looked just like them!