You don't have to like him, or even respect him. I'd be quite the hypocrite to piss all over Leslie Nielsen's memory and then bitch because somebody said something mean about John Lennon.
However, I find your comment disingenuous. I can't believe that you didn't "notice" when he died (I assume that's what you mean. Not that you weren't aware that he'd been dead for the past thirty years). Even as a child, albeit the child of Beatles fans, I could see that the story was all over the news at the time. This was not treated by the media like the passing of some also-ran pop musician. This was more akin to the death of a Head of State. The death of John Lennon was treated, by the media and populace alike, as equal to the death of JFK or Martin Luther King, Jr. Because the story here was not merely death, or even untimely death (Kurt Cobain, Jimi Hendrix, Keith Moon), but VIOLENT, untimely death. Whatever you thought of the Beatles, John Lennon's death was BIG, BIG NEWS. You noticed. Or did you also not happen to notice 9/11?
"Hey, didn't there used to be a couple of towers over there? What do mean, 'where have I been'?"
I can see missing George Harrison's passing. It wasn't quite the same level of news story. But missing John Lennon's death? Do you have ANY memory at all of 1980?
Maybe that comment was a bit too flip, let's just say Lennon's untimely passing still isn't that significant to me. I heard about it on the radio the next morning while I was buying my Dad his birthday present.
Now Harrison's death...that was real sad.
Comparing it to 9/11 plain fucking silly. The Beatles are pretty trivial in the big picture. I could see the twin towers from my building and was on my was to town on that morning.