Pressure is a key part of the barista's job. It's necessary to pull espresso, steam milk, and deal with the crowds.
Different sorts of pressure are, of course, applied in each circumstance. All are essential, however. Perhaps, one could even call them routine.
This is true, in so far as the first two actions are performed often enough that they become second nature. Milk can be stretched by sound, or touch even, given enough experience. Even the crowds, so daunting at first, become part of a comfortable routine.
But there are situations, still, that can throw even the most seasoned barista off their game.
The first, and perhaps most obvious, is the crafting of a drink for an individual who, let's just say, strikes the barista's fancy. Perhaps you ramble a bit more than normal, your co-workers wondering what the hell has gotten in to you. You trip, spill milk, then stretch it too much -- and oh fuck -- you totally forgot to pull the shot, and toasted the grounds to ash. Even still, you limp towards the finish line, hoping against all reason that maybe you can get a latte art heart on the drink. Tada! A amorphous blob. You finally hand over the drink, which by the way, they wanted iced.
Coworkers and bosses can be tough customers, in so far as you want to make something extra special for them. However, assuming that they actually like you in the first place, this interaction should be a casual and friendly one, resulting in an easy to prepare drink.
Fellow baristi, who work for other shops, however, are much more difficult. You have the constant, nagging sensation that they're evaluating everything you do -- judging your every move. Poured too much milk. Steam wand too deep. Shot too fast. Pour too rapid. If, however, you do get everything right, your coffee sibling tends to appreciate your work more than a less educated customer might.
Which brings me to the most pressure packed situation of all: The totally clueless ass hole. In the aforementioned situations, there are possible pleasant outcomes. There are ways in which you can hit all the right notes, and strike up a pretty nice tune. Not so, in this case. No matter how you make whatever it is that you make, you will do it wrong. In fact, you will make a drink totally unlike what they wanted. You are such a dolt that you can't even comprehend what their totally obvious drink preference is. And what's worse, the drink you make sucks. It tastes horrible, is too bitter and too sweet and too watery and too foamy and just fucking WRONG.
You should probably go dunk fries for a living, except that you'd fuck that up too, somehow.