Finicky Mountain Lion wireless?

Once again, a question for you all.

But first, some specs:

Model: MacBook, 13-inch, Aluminum, Late 2008

Processor: 2 GHz Intel Core 2 Duo

Memory: 4 GB 1067 MHz DDR3

Graphics: NVIDIA GeForce 9400M 256 MB

Software: OS X 10.8.5:

Alright.

For the longest time, I had smooth sailing with my MacBook in terms of wireless. My range was fine, I could hop onto connections with no issue. So why has my laptop decided that it HATES my buddy's connection suddenly? And several connections around the same geographic area.

Literally overnight I went from easier joining his network to "Unable to connect". The airport icon will search up and down, up and down and just...grey out. If I'm lucky, I'll get to the password screen. Where it will grey out once again. Several of the neighborhood networks produce the same result, but my home network? Not a single issue. Big box store wifi? No problems. All of the other devices in that household can find the connection just fine and hop on, including my Kindle and Windows netbook.

So does anyone know why this is happening? The "Geniuses" tried setting a new location for my wireless and that did squat.