Tweezers.
If that doesn't work, you can try a dab of superglue on the tip of a stick (the plastic frames that hold model pieces is ideal). Just be careful to make sure the stick and glue only touches the plastic shroud you're trying to remove.
The most stubborn stuck piece of plastic, I removed by heating a butter knife over a kitchen stove, then applied it to the stuck piece and a plastic stick until both began to melt. Then I mashed them together and let them cool to form a weak bond, but strong enough to carefully pull it out. Not sure I'd recommend this though, as there's a lot of potential for damage or injury, and you pretty much ruin the knife.
I thought the shroud of a USB plug was metal. And the pins were inlaid on the plastic piece? If it's the shroud that's stuck, and the middle plastic tab with the pins is out, then the superglue trick is probably your best bet.