A few years ago, while surfing the internet late at night under the influence I happened upon a very cheap flight to Basel, which has always fascinated me due to its location on the border with France and Germany, and a week or so later I did:

CH - FR - CH (on foot)
CH - DE - CH - DE - CH (the latter 4 crossings were on a scheduled bus route)
CH - DE - CH (on foot, the only time I got stopped and questioned)

Geographically the airport counts as FR - CH - FR, but not from a border control point of view.

I'm sure someone here will have done more.