If it's in the EU, opt-outs are permitted, and they will result in a thorough pat-down. It's your choice if you want a private room or not. However, some airports/staff are more willing to give you the opt-out than others.

The UK airports with body scanners are particularly known for doing this. They will deny that an opt-out exists until you ask them to get the manager, who will then tell you that an opt-out does exist, and threaten you with the laws changing in the future. You will then be given the same frisk search as if you had triggered a metal detector as they were before. No, we don't understand why this happens every time, either...

In the past 3 months, Germany has had a major security 'crackdown', in which body scanners are being placed at all of the major airports, and being used on most passengers. At CGN, FRA, and DUS, the scanners are almost everywhere. At MUC, I think they are still only used on US-bound flights, as you said. Staff may deny the existence of the opt-out, and you may have the UK-style experience described above, instead of the Dutch experience, which is an immediate acceptance of your request to opt-out.

Check the two main forums dedicated to this topic:
http://www.flyertalk.com/forum/pract...y-scanner.html
and also
http://www.flyertalk.com/forum/pract...er-2013-a.html