Customers. I work in a supermarket in the produce department and the rudeness I deal with every day makes me feel, well, murdery. They say youths have no manners but 90% of the rudeness I endure comes from elderly customers. I used to work at a fast food restaurant and it was the same there.
The thing that annoys me more than ANYTHING at work is this:
Me: *carrying extremely heavy tray of cucumbers* Excuse me!
Customer: *continues rooting through trays of identical cucumbers*
Me: *arms starting to ache* Sorry, can I just...
Customer: *appears to have found the perfect cucumber but OH... NO... puts it back*
Me: *wrists about to snap* Can I just squeeze in here?
Customer: *tuts, looks at me with disgust and walks away, cucumberless*
Me: *collapses*
-.-