Going out on the town with a group of veterans is definitely an experience that all civilians should try at least once. Not only will it dispel any preconceived notions that a civilian might have about the troops — we're not all crazy, loud as*holes — it's also a crash course in military culture and etiquette.
It's the best way to learn all of the little details, like where veterans naturally position themselves in a bar (to get a better view of everyone coming in and out) and how they'll instinctively form a wedge formation as they walk (a secure way of moving from one place to another).
After you've settled in and you're throwing back a few cold ones, one question that's sure to surface from the civilian tag-along is why veterans solemnly make a toast and tap their drink or shot on the bar before resuming a night of heavy drinking. This tradition actually has roots that extend all the way back to ancient times.
The toast is a piece of international bar culture, but the military takes it to the next level. The first part is standard: Someone raises their glass and either dedicates the drink to group's collective health or says something silly like,
"Life is a waste of time, and time is a waste of life. So let's get wasted all of the time, and have the time of our life."
This brief, poignant message is a way for the person making the toast to appreciate everyone with them. If a veteran is giving that toast, they'll next tap the drink on the table or bar to appreciate everyone not with them — the fallen. Think of this as a less-messy version of pouring one out for the dead. The veteran first shows respect to those around him or her, then to their fallen comrades, and then, finally, to his or herself by knocking one back.
It's also seen as a sign of respect to the bartender and the house — who are some of the select few people that a veteran never wants to anger. This same tradition was also seen in ancient Irish times as a way to scare off evil spirits.
So, if you see a veteran do this, by all means, join them. Keep the moment solemn as they are, nod, smile, tap your drink with them, and enjoy your night.