I'm going to curse out the convenience store guy
Why would it ever be okay to curse at the convenience store guy?
He's a really rude bastard.
You shouldn't be rude to workers even if you feel they're rude to you. Maybe you can find another store to visit if the worker bothers you. This might be less stressful in the long run.
Look Dick, I have to deal with this loser all the time, If I wanted to be nice to him, I would have to take a shit.
It's really not okay to curse at people who work in customer service. These days especially it's really stressful, and customers should be trying to make their jobs more pleasant, not less.