What is a word or phrase to describe a forced smile from someone who is not practiced in smiling?
Solution 1:
I would call such a smile a "Pan Am smile".
The Pan Am smile, aka the 'Botox smile," is the name given to a fake smile, in which only the zygomatic major muscle is voluntarily contracted to show politeness. It is named after the airline Pan American World Airways which went out of business in 1991, whose flight attendants would always flash every jet setter the same perfunctory smile.