If you JUST want BB rep, kill the pirates outside BB. This will give you a little bit of the other goblin reps as well, but I wouldn't try to raise Gadgetzan by killing the pirates outside BB.
If you want all the goblin reps to raise, then you have a couple quests to do. One is out in Feralas, the zapping giants quest. The other is in Dire Maul. You need to find the key for the goblin that is in shackles. The key is unique, so you can only have 1 key at a time. If you're doing this, I'd suggest getting one key and opening the shackles. Then go and clear the rest of the instance to see if you can find another key. Once you find a second key, leave the instance and reset it.
Doing these two quests will not lower your Pirate rep, so if you are going for Insane, this is what you will have to do.
if at first youre lower than neutral, start by killing alot of the bloodsail buccaneers or other groups of pirates threatening steamwheel cartel, once at neutral or friendly, do alot of the quests in booty bay