There’s an improv game where you make goofy faces at someone when they’re not looking. They’re doing the same thing to you.
This game has roots in comedia dll’arte. The way I originally learned it was with three performer sitting in a row. The outside players would attempt to make faces, the middle player had a balloon slapstick and would smack them if they were caught making faces.
It’s good practice for quick reactions and for keeping your performance playful and fun.
I like to do this in public. It’s a bit more challenging than on stage as your potential audience might be anywhere around you. You can play it either by avoiding being seen by the person you’re making faces at, or by anyone who might potentially see you. The second way is a little more difficult.
I advise that you keep the faces goofy and silly. Although, I have found it amusing to make a burning anger kind of face. Like the person owes you money.
Why do this in public? Couple reasons. First, just to keep life interesting and fun. It’s really harmless fun, especially if the face isn’t aggressive (don’t want to freak out someone who catches you). Also, it’s good practice to get caught looking or acting foolish. The more times you get low-level embarrassed on your own terms the easier it is to act a fool.
Many people are worried about looking “foolish” so, lean into it. Be the fool. Own it. Have fun.