Because they are losers with big life problems.
or
Because you fallow them and talk too much asking if they need help ect (but that's not your fault because your boss is probably pushing you to be this way)

Being rude at a sells person or a cashier is very low.

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office supplies

office products

Simple. These people have nothing in their lives will be in them, and the other (if any can be treated like crap without the repercussions because) gives them a sense of power for a brief moment.Trust me, I've been in years for customer service, and I have psychology.

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flower seeds|plants by post