I too have initial + last firstname.lastname@example.org and get a fair amount of misdirected email. I make some effort to find the right address (had to call someone who accidentally had her cell phone bills sent to me... Happened about 2 weeks after the XKCD cartoon.)
But I don't assume laziness, stupidity or malice when someone uses the wrong address. It's just a mistake. And people are almost always grateful when you help correct their mistake.
It must be a miserable world where everyone else's mistakes are due to critical character flaws. You have my sympathies.