It seems like the stress should be low, right? The boss isn't usually breathing down your neck, and what's the worst that can happen? You take too long to serve someone their beer? Pretty low stakes. If you want on-the-knife-edge stress, go check out our brain surgeon career guide.
However, things can get a little intense. If the bar is totally packed and a few guys get drunk and into a shoving match, you might have to step in. Even when things are going normally, you have to move constantly and you're always having orders snapped at you. Let's call the stress level for this one a solid six out of ten.