The customers that annoy me most are the ones who assume they know how to do my job better than I do. On the rare occasion I'm on bar they'll stand and stare, of course, but they'll also butt in and try to coach me through each step of making their stupid mocha-extra-caramel-bullshxt-concoction.
"That's FIIIIVE pumps of mocha, now. Make sure the foam isn't too bubbly. Don't let the shots sit there too long!"
Listen d-bag, if I wanted to listen to that I'd make a recording of my manager saying the steps and play it on loop. Now trust the "certified" pin and hop off!