Fractious fruit men

"Have you ever noticed," Delta mused the other day, "how the fruit sellers on street corners are always so unfriendly?"
"Huh?" I had to confess, observant though I may be of the nuances in life, the assessment of fruitseller dispositions had slipped by me.
"Seriously," he pressed on. "I go to the same fruit guy every morning, and I greet him every time, and he doesn't even acknowledge me!"
"Does he recognise you?" I snickered at Delta's personal affront.
"Obviously." We were passing the fruit cart by Delta's apartment right then, and he threw the fruit seller a dirty look for good measure. "It's just so frustrating!" he pressed on, "why can't they just be friendly!"
"What about your new apartment? You've got a new fruit man now."
Delta gave a dramatically tragic sigh. "He's just the same."

"Grumpy Grape guy," he said.
"Pugnacious pineapple guy," I rejoined.
"Ornery orange guy."
"Stroppy strawberry guy."
And so we continued until we had exhausted our fruit and adjectives. At least it made us feel better.

This morning, I stopped to pick up fruit at a corner fruit cart on my way to work. I decided to put the observation to test.
"Hello!" I wished the fruitseller brightly.
Grunt.
"Thanks," I added, as he handed me my fruit in sulky silence.
Grunt.
"Okay you have a good day then," I concluded our conversation mutually, in a reversal of customer service etiquette.

What is wrong with them?! This is even worse than the subway staff (and I have a personal bone to pick with the subway staff). Must be something they are taught in fruitschool.