I'm particularly amused by the line "woah, you're me!" Now, I have never been visited by a future version of myself, so I can't say this for sure, but I suspect that I wouldn't respond with that phrase. I might not even recognize that the person was me, because I would think it so very unlikely that this situation would arise. In the world of xkcd, however, everyone looks exactly the same, and so there's no way to tell if two characters are in fact copies of each other or if they are two completely different people. Thanks again, xkcd art!
Next, Panel 2 has a similarly dumb line like that. Think about it - if you went back in time to kill your previous self and prevent them from inventing a time machine, would you announce to them exactly what they were about to do, or would you just kill them and get it over with? Again, I have never been in this situation, so when I say I would not go through the exposition seen in panel 2, I am merely speculating.
The real problem, though, is that this comic is based on the idea that such a situation is a novel one. And it's obviously not. I try not to link to Abstruse Goose too much because I hate it, but this recent comic really is quite similar to today's xkcd. Look at them - not only do they end with a bloody object as the only color in the comic, not only do the end with future self killing off past self in order to replace him but both even that post-script sort of explanation stuck just below the last panel. I like the Abstruse Goose comic more, by the way, for two reasons: one, it has the humorous exaggeration of learning basically all possible knowledge, and two, because it's not only making a time travel joke, it's mocking the idea that you could learn C++ in 21 days.
Of course, there's another source out there that some of you were reminded of with this comic, namely, the movie Primer. There're gonna be some spoilers here, incidentally, so you are forewarned.
Primer has this happen all the time - both main characters have to go back in time routinely to kill (or just knock out, it's unclear) their past selves and replace them - sometimes while they do this they run into other versions of themselves trying to do the same thing - it's all very complicated and weird, but the point is, it's been thought out before. And of course, we know Randall is a fan of Primer, because of this.
Anyway. This isn't the first comic where Randall's thought of an old idea and pretended it was original, but it's one of the lamest. The joke rehashes an old idea while adding so little new of substance that I consider it more pathetic than anything else. It's been a really terrible few weeks for xkcd, and I am perfectly happy to take a break from it. Person #1 - editor of the xkcdsucks book! - will be writing all next week and I'll return after that.
SEE YA REAL SOON, KIDS!