There's a Reason Part-time Clerks Leave After Four Hours.

In my short time as a courtesy clerk for my store, I've found that after working for about three-and a half hours, I start to direct all my thoughts toward the things that until this point, were only mild annoyances. About a minute after, those little hairs trapped in the nape of my neck transform into a super-itchy iron maiden that lingers on in spite of my manic scratching.  That cramp in my leg is now a mafia boss smashing my knee in a vice coated with rusty nails.  My managers evolve into genetic amalgamations of Hitler, Mussolini, Stalin, and Genghis Khan.  Even the costumers' simple questions feel like vocalized crowbars, slowly prying away at the nails of my psyche. There's a reason the four hour mark was unanimously dubbed the time to go on an hour lunch during a full shift, or go home to shovel leftover turkey burger in my mouth on part-time days.  Once three hours and thirty minutes of unbridled altruism and kindness have passed, most people have reached their capacity for this sort of crap, and with the only methods to refuel my tolerance being a chronological crawl away, my personality inevitably spirals downward with enough angular momentum to slice open a customer's chest cavity.

I don't think this feeling is unique to me either.  A number of coworkers I get along with share the sentiment, or at the very least, don't disagree when I come into the break room announcing "I'm itchy, I hate everything!"  I do know that some employees are generally rude, but for most of us, the only reason our happy face fell off right at the moment you came asking for help is merely the result of a common phenomenon where we're trying to be nicer than evolutionarily possible.