I got an ep[iphone sg, I got it so I could play ac dc, hells yeeeaaah, but there's something wrong with it, when ever I plug in the cord, it ends up falling out of the guitar, and I don't really understand why

Remove the input from the guitar.
The long piece of metal is the part that holds the cord in it is bent over too far and won't put force to hold the cord in. bend it back and put it back on make sure not to pull the wiring off or you will have to solder it back on.

The guitar cable is too small that's all. Just go back to the music store you got it from, return it, get your money back and buy a new one that fits in the cable input on your guitar. Almost every guitar needs 1/4 inch cable input. Yours is probley an 1/8 inch, those are for hooking up speakers or other electrincs. Go with the 1/4 inch cable my friend.

Yeah, return it.. My brother had one of those, he didn't like it, I think he ended up smashing it on stage..

One more Clint line...
"If you're going to be a lumberjack, you've got to carry your end of the log."

Check out you'r local music shop... shreves maybe right.