Here's as far as I'll spin my wheels over this kind of question any time one shows up on the Internet (since I'm way past the stage in life when these kinds of questions tend to be the big thing, since I'm not one for "mind-expanding" substances, and since my offline and Earthly existence takes up pretty much all of my time)...
On the Internet you don't know who really exists and who doesn't (which is why the person who wants to make it clear that he exists needs to be a few extra efforts if one hopes to reassure someone else that he's not dealing with a giant fake/illusion (or whatever).
With regard to offline life, my reply to "the old exist" question is always my personal reference, the ever humble row of saltine crackers that are usually somewhere not too far away from me. If I take out a new row (four rows in a box, of course) and start eating the crackers there will be permanently be fewer crackers when I finished snacking on them than before. In fact, depending on how many were in the row, the crackers my even be completely gone at the end of "snack time".
If you happen to be at the table with me, having coffee or tea (and maybe even crackers, although I don't usually serve guests saltines, but that's not the point, is it..) you'll witness the "disappearance" of the saltines right along with me. You and/or I can see the reality of the saltines, and if we count them we'll come up with the same number (assuming, of course, that one or both of us is not using some kind of mind-affecting substances).
Not all reality is subject to perception; although if you aren't in the room with me when I get out the row of saltines I can tell you all kinds of baloney about how/why they disappeared. In fact, I can really try to freak you out and tell you that neither the saltines nor I really ever existed (and by the way, neither do the other two rows in the box).
You don't really need to now that I exist, and I don't really need to know that you do. We're killing time and/or doing whatever we do on the Internet. It's probably wise (and I mean "wise") to have a realistic idea about whether the saltines were left by The Saltine Fairy or baked by The Keebler Elves (although sometimes all we need to know is that there used to 30 saltines and now there are none).
Not to sound self-righteous, but one reality is that we live in a world where some people are starving