The spider shake, mostly used by teenagers, is the act of picking up and violently shaking an article of clothing before wearing to remove any spiders which may be hiding inside. This is necessary if the article of clothing was stored in a particularly messy place.
Mother: "Alex! I just saw a brown recluse crawl out of that pile in your closet, be careful getting dressed!"
Alex: "it's fine, I always use the spider shake."