Here, - for total appreciation of this post, you should - have a look.
I have suffered with this most of my life although it's not so much a Resting Bitch Face as a Resting "Cheer up, it might never happen" face. (That would be - RCUIMNHF - not such a good acronym.It won't catch on.) Seriously though, the minute my face isn't working to express what I'm saying - which, let's face it isn't often, as I talk a lot, and the Ball & Chain says there's no filter between my brain and my mouth - it looks like I'm carrying the weight of the world on my shoulders. I can't even put a mental shopping list together without someone asking if "everything's OK".
And, because of this, I have a theory about Americans - Resting Bitch Face (or it's many variations) is why they smile so much. (At this point, if you haven't clicked on the link above, you may find yourself lost - you have been warned.)
A good 50% of us are RBFs (or, like me RCUIMNHFs - def have to come up with a better acronym - answers on a post card please.) So - being the friendly, accommodating people they are, Americans over compensate, like # 13 - being "extra peppy", or #14 - doing the "fake smile". (Taken off the Brit list but done all the time. ) Exhausting, but worth it if you're bothered about offending people.
In my experience, Brits don't give too much of a flying you-know-what about who they offend with their facial expressions, indeed, non-verbals are a weapon of choice. Americans, however, really do care - Hence the smile factor.
Love you Donny, but there's "that" smile. 
Hmm - who knows what's going on here. Brits on the other hand - either don't care about looking smiley -
I have disdain for everyone - on the planet.Or don't care AT ALL what how they when they have their laughing face on -
OK, looks like an otter, but still adorable. 
