By far the best reaction is that guy towards the front, in the blue flannel and ball cap, who takes a quick look at Smith over his shoulder but then immediately directs his eyes back to the empty stage.
That studio audience is the gif(t) that keeps on giving, as it shows the massive joy Will Smith inspires upon entering an unsuspecting crowd zone.
What was going on with The Roots that’s cooler than Smith hyping up a crowd?
Regardless, he seems to be having a good time, and that’s really all that matters.