Headcanon: It has to do with PTSD, seven years of war, this being the first public occasion where he has to represent again not in front of the soldiers but in front of civilians and the alas tried and true kicking down mechanism of stress relief.

re: "maman" - he uses that from the start!

That is fascinating. Especially since SD was so much on the lookout for possible rivals in her son's affections otherwise - I mean, the entire early reaction to EC was based on that as much as snobbery (hence it settling down once Fritz had made it clear that SD would come first in Prussia nad with him). You'd think she'd resent Fritz calling someone else Mom?