When a pair of breasts have sagged to the point that you can fornicate with both the breasts and vagina at once. Depending upon the age of the 'sandwich meat', you may be able to introduce a prolapsed or distended anus as another condiment, thus making a Club Deluxe Sandwich. Most sandwiches come 'sans mayo' but that, being the point in engaging in said activity, is usually easily remedied with a quick glazing.
"Slide that diaper down real slow, put the walker over there. I'll plug in your Rascal... there. Now lets touch your toes and have a Club Sandwich