The constant smile and happiness is odd. I don't think sims feel REAL happiness if they are "happy" all of the time. I think fine should be the default emotion, it is more realistic.
The constant grinning will never NOT annoy me. This has been an internal complaint of mine throughout the life of ts4. I make way too many serious or mean sims for all of that grinning. Looks goofy lol. Neutral look should be default. Grinning only if very happy.