I'll reiterate that I think the whole "Well, Riker wouldn't..." is a completely false equivalency. Riker has a different relationship with Picard, was a different type of officer and simply wouldn't find it necessary. Raffi obviously did, or enjoyed the nickname, or other reasons.I'm going inconvenience everyone by bringing this thread back on topic.
Someone said that seventh season Picard might've let "JL" slide. I don't think so. At least not if it was serious. If it were a one-time joke, he'd let it slide. But I don't think "JL" is something Riker would call him because we didn't call anyone by their initials.
None of which mean that Picard is acting out of character or whatever other complaints. People change over 20 years and relationships between people are different with different people.