Upvote:1
Not a good idea in non-EU/EFTA countries, as they can refuse you entry for any reason they like, and a grumpy officer may perceive your odd wish as suspicious behaviour.
Much better to ask for a German stamp - the Bundespolizei can hardly do much more than say no. I collect stamps on a blank sheet when in the mood (I use a Swedish ID card) and the Germans have always given me one when asked.