So I finally got pissed enough after almost lagging out and dying in Maplestory to open up the logs, and I see a giant list of incoming connections from port 4803.
I had previously asked my little brother if he was downloading anything, or was experiencing any lag last night, and he was like "no" every time. So when I went onto his computer and saw LimeWire (which, although I disapprove of, I'm not going to confront him about it) set to consume 100% of the bandwidth.
I don't know what he was thinking, but I've done the best I can to close port 4803 (the port currently used as an incoming port) during the hours I'm normally online, as well as disabling uPNP. I'm seriously pissed off though, not because he was consuming all the bandwidth, but because he lied about it when I was trying to figure out what the fuck was going on.
I've decided to return the favor though, and not tell him what I've done. If he switches ports, I'll block that one too. And if he switches again, I'll block his MAC. Sucka.
It pays to be in control of the network.