How can people be so awful? 😡😢

Ke
I was just at the gas station prepping my car for a 10 hour drive tomorrow.  I had finished filling up the tires with air and realized my windows were a little dirty.  The gas station I was at had been dead the whole time I was there and there was only 1 other car there at this time.  So I drove from the air pump over to the gas pump, grabbed the squeegee and cleaned my windows.   
While I was cleaning them, two other cars pulled up.  One of them was an old man who pulled up right behind me.  The entire time I cleaned my windows he berated me to the other people filling up their two cars. (Who said and did nothing during this, so I don't know who's side they were on)
"Can you believe this? This a***hole of an idiot holding up a gas pump to clean her f***ing windows. What a b****!" 
(Just an FYI, There were no cars waiting for a pump) 
I remained silent. 
"Oh yeah, just go on. Keep doing what you're doing. You're not holding anyone up."  
He proceeded to clear his throat over and over until I turned around and said "Sir, your car goes in reverse. You have enough room to get out the same way you came in." 
He scoffed and called me a "f***ing moron." 
I got in my car, flipped him the bird, and drove away.  
And now I'm home in tears partly because of how he treated me, and partly because I feel guilty over losing my cool at the end like that despite telling myself to keep it together, and partly because I didn't realize there was an unwritten rule that if you're only going to clean your windows, you have to park your car on the other side of the lot and walk the squeegee over to it.  I just don't understand how there are people in this world who can treat someone that way and I feel like I'm no better than him because of how I reacted.