Yes, they came up for pay at the same time, but they didn't all work the same number of hours. Some worked the full 12 hours, some came at the eleventh hour and only worked one. The complaint was that the ones who came in late were first in line to get paid and they got a penny, so the ones behind them that had worked longer hours figured they would get more and they didn't, they got the same amount.
"Is thine eye evil, because I am good?" Seems it would mean that he was saying that they were upset because he was generous with those who only worked an hour and gave them the same pay, so they were lookin' at him like that was a bad thing.
I'd relate it to us by saying that those who have been Christians a long time might get upset that new Christians get blessings and are received as brothers and sisters as much as those who've been in the family for years and years.
The point would be that all of our work is for Christ, and we are as precious and equal in his site and of value whether we've been working for him all of our lives or for just one day. :)