Here are 2 dudes in Jamaca. Dressed for the beach. But they have knives on them.
In a social setting: Before something gets escalated to the physical, remember that the other guy might have a knife.
Not many people around: Somebody walks up to you – check his hands. Specifically his palms. If you can’t see his palms (behind him; flat against his leg; hand in pocket; under armpit) then what’s he hiding from you?
Knife attack in front of lots of people: You’re either in the wrong kind of neighbourhood or the wrong lifestyle – change as quickly as possible.
P.S. Is that one dude wearing a WW2 helmet?