rabbiofberlin,
The Bach (Yoreh De’ah 182) says if it is needed i.e. it is raining and the only raincoat available is of the opposite gender, it is permissible to wear the opposite genders clothing IF one is not FULLY dressed like the opposite gender. Perhaps this is what you refer to. The Rambam disagrees with this Bach. In any event, it is only applicable in those conditions I mentioned, not a blanket heter.
And like I pointed out on the previous page of this thread with the NUMEROUS listed mekoros, that the consensus is very clear against.