Act busy, even if you aren't.
Act like you have to hurry somewhere even though it's absolute tranquility inside.
It serves to let people know you're overworked, don't have time to spare, and get busybodies to leave you alone.
Some people say the world is your oyster.
I personally doubt the veracity of comparing the world to diarrhea inducing seafood.
Whatever floats your boat I suppose.