Sam Smith and his boyfriend, Brandon Flynn, put on a smoke show ... literally.
The Grammy singer and "13 Reasons Why" star snuck in a quick cigarette break -- and a kiss -- Wednesday night outside of Gemma restaurant in Soho ... where the couple dined with a few friends.
PDA was definitely calling -- Sam had just returned from Japan. Their silly sides were also on full display ... walking an imaginary runway with different strides.
It might have gone down something like this.