You have to account for the different types of excuses, too. There are those dealing with oneself, those dealing with another player, and those dealing with something external (which includes lag, framerate getting killed [by IRC, perhaps

], kids pulling out networking cables, etc.).
In the first instance, it's usually a matter of someone blaming himself for a mistake. "I did such-and-such and therefore messed up." If it's true, or there's no reason to disbelieve it (spite or self-righteousness doesn't count), I'm curious how one admitting his own mistakes is lame. I'm especially curious how it's equally as lame as completely making something up for an excuse. Please don't tell me it's some "personal responsibility" ethic.
As for the other two types, face it: sometimes it is legitimate, particularly in the last instance. In these cases, like the first, it's explanation, not necessarily excuse. It's just a matter of judging the individual and the claim as to the liklihood of it being true.
However, if the claim, whatever the sort, is easily remedied, yet the claimant does not remedy it, then that is rather lame, in its own way.
Oh, there's also a fourth type: those where the person is simply confused—blaming one thing when it was actually another. Those can be annoying, especially when you've explained what it actually is and they deny it to try to save face or whatever.
Eh, whatever. Yeah, illegitmate excuses are made. Some wankers repeat them over and over again. Some have one for every time they're cored. They're dorks. Sometimes it's funny. Sometimes it's annoying. It's a video game.
By the way, I agree with Fonkay. I find that a significant discrepancy in ping, whichever the direction, can be a "challenge." And I personally tend to have more difficulty when my ping is significantly lower than another's.
And I do find amusing the sort Sab referenced:
"You think you're so good. I could beat you easily. I'm just toying with you. I'm not even trying."
OK, but I think you're lying.
"Alright, it's on noob! I'm gonna own you LOL!"
Nothing changed.