Orchid,
Tis not paranoia, but caution.
I doubt that most of the posters here have worked in a job where their clothing made them an easy target during working hours. Lessons are passed along from those who survive an incident or those who listened to those survivors. Hence, the "face the door" or "back to the wall" thinking posted by many.
When dining out, if my dining partner strikes me as someone who wouldn't notice a six-man mortar team setting up in the lobby, then I'll sit facing the door or having a good view of the area.
If they have my confidence then I'll sit wherever is comfortable or left to me. I don't "worry" about it as much as I simply make it habit.
If you look up the San Ysidro, CA killings at the Mickey-D's there, survivors talked about seeing the man approaching with weapons ...and waiting to see what he was doing with the guns. I would have been heading to an exit.