A wooden toothpick is probably a bit too thick. You'd want something thin enough that it can be inserted without touching the electrical contacts. If you do have something plastic then that's probably better, but if you do the cleaning when the device is off the USB port should be unpowered and there shouldn't be a risk of causing a short, and modern USB ports are quite well protected again shorts anyway so it's very unlikely to cause damage just by being conductive. You mainly want something that is long and thin enough to get all the way to the bottom of the port without having to apply any force. If the only things you have that are long and thin enough to reach the bottom of the port without having to be forced in are made of metal, then that's still a safer option than jamming something too thick into the port that can deform the center contacts.